How much would it cost to get started with Magic: The Gathering?
There have been many answers to this question, as there are many different ways to handle getting started in magic. Really, the best thing to do is to explore carefully and decide how you are going to play that's the only way to get a feel for how much your initial investment will be.
First and foremost, as others have suggested. Regardless of how you want to play, as a new player, Duels of the Planeswalkers is a fabulous way to get a feel for how the game is played. It's available on many different systems, most consoles and PC, as well as some tablets. It gives you an excellent way to get an idea of what different colours do, how they interact, the beginnings of how to use your resources correctly and the best strategies to employ in given situations. If you want to know whether you will like the game at all, this is the best way to find out.
If you like the game enough to continue from that point to the next step. There are 2 options, Paper magic, and Magic Online (often referred to as MODO). both of these are open to casual and competitive players alike, and the decision comes down to whether you are going to want to play with friends in your local area, with a hard collection to show for your money, or be able to jump in to a game of magic any time of the day or night. Whichever you choose, you will be making a similar level of initial investment, so your choice here really counts!
If you choose to take the online route, then jump onto the internet and make yourself an account, there are plenty of resources out there to help players get started on MODO, and there are bots who will give new players a handful of free digital cards to help grow their collections initially, besides that, you can buy boosters and enter tournaments just like with paper magic. you can even cash out your digital cards from recent expansions into paper copies if you complete a full set. If you go down the route of MODO, your initial minimum investment will be in the region of $10 for an account, from there you can jump straight in to playing some games.
if you choose the paper Magic route, then you need to make a decision about what kind of Magic you are looking to play. This is a very subjective choice, and depends massively on the player, realistically, without doing a bit of experimenting, you will struggle to figure out exactly what you want to do with magic. I will expand on this below:
Casual Play
There are many players (in fact, the vast majority) who will happily buy a few boosters here or there, and then build whatever decks they fancy out of what cards they have, and battle with their friends. These players get a lot out of every single card they own, and generally open a few boosters here and there a few times a week. Players like this will be playing at home with their friends, round a kitchen or dining table, with whatever decks they put together for that evening, maybe building a deck in a different colour for each of their friends that come to battle.
If that is the kind of magic you are looking to play, then your initial investment will not be sky high, there are many good answers already covering this, so I wont paraphrase them. I will say that sealed product (boosters/starter decks etc) would be your best choice. You would be able to spend as much as you feel you want to to get a collection big enough to build what decks you need to have fun with your friends, this could be as little as $20 as others have suggested, or I would say up to $100 would give you a very good basis to work from for a larger pool of cards to play with.
Like Competitive Play described below some casual players choose to follow certain deck construction rules (called a format) when building their decks. One of the most popular formats is called Commander, which involves creating a deck around a specific Legendary Creature, called your Commander. These decks are 100 cards (99 + the Commander), you can only have one a given card in a deck (other than basic lands), and all cards in the deck must have a color identity that is included in the commanders color identity. There is a Commander special release every November with 5 new decks that are around $35 a piece and are usually fairly competitive (for a casual audience, they aren't Competitive in the sense they would do well in a tournament).
Competitive Play
If casual play at home with friends doesn't sound like your thing, (either because your friends aren't interested, or you are looking to meet loads of new people to play against, or you want to play to win) and you are looking to play in tournaments, then things go a lot differently, both in how to get started, and how much your initial investment will be.
There are many different types of tournaments, Limited formats, which require no prior investment whatsoever, are a good way of entering tournament play without having to spend any money prior to the tournament. You get the same chance everyone else gets, and it all comes down to learning how to play that format (be it draft or sealed) better than everyone else. Entry to these tournaments is often more expensive than traditional &quot;build a deck beforehand&quot; constructed tournaments, but you get to keep the cards you use in the tournament, so its a good way of picking up cards to expand your collection, whilst playing competitively. The cost of draft or sealed tournaments varies, so your local store is the best place to find out more information about this style of play.

If you want to know more about the types of tournaments, and advice about them, continue below, however, there is a LOT of information to process, and if you already feel like casual play is more for you, then this information is of little use to you. have fun YOUR way, and at YOUR pace!

Limited
As previously mentioned Limited formats require no prior cards, you play with the cards you are given by the Tournament Organizer. For limited events you have a 40 card minimum deck size rather than the 60 cards needed for all the constructed formats.
Booster Draft this is the most popular form of limited play. The way it works is you are seated at a table with several other people (8 players per table is considered ideal, however numbers can differ based on tournament attendance). Each person is then given 3 booster packs, they each open one of their packs and keeps a card from it passing the rest to the player on their left. They then take the pack passed to them from their right pick a card from it and repeat this process until there are no more cards to pass. This process is then repeated for the second and third packs, alternating direction with each pack. Each player then makes a deck from the cards they chose.
Sealed Deck is the other main form of limited play. In this format each player is given 6 booster packs and has to make their deck from the cards in those packs. This format generally has a lot more luck than Booster Draft since you only get to see 6 booster packs vs 24 boosters you get to see in draft so if you are unlucky and get bad cards there isn't really anything you can do to mitigate it.
Constructed
Constructed competitive play is a whole different ballgame. This is where things get different, as in terms of &quot;bang for your buck&quot;, you are best off buying individual cards from a reseller, rather than opening boosters and hoping to get the cards for your deck.
First and foremost, Event Decks have been made especially for you. they are more expensive than starter decks, but with very good reason. They contain more rare and powerful cards, and are generally built so that you can have a hope to compete in a tournament with them right out of the box. They even have instructional inserts to explain how the deck is meant to be played, and giving you some tips on how to use the cards that are included to best effect! These decks serve as an excellent starting point to build on. Note: Event Decks were discontinued with the release of Battle for Zendikar.
Playing at this competitive level, especially as someone starting out, it is very important that you start by paying attention to what kind of decks are winning tournaments week after week. There are plenty of websites that will give you a list of the decks (and every card they played) that came in the top 8-16 or so of the tournament. This gives you a very good idea of what kind of decks can do well reliably, and hence what you should be looking to invest your money into building. You can of course disregard this and build whatever you want, but if we are talking about investing $200+ in something, it's probably best to go with a tried and true formula, at least until you have some experience.
You may want to pick one of the cheaper decks that performs well, so you don't have to spend quite so much so soon, and that's fine, cheaper does not mean worse, and you can build something quite playable with under $100 if you pick carefully. You can also replace some of the most expensive cards with something more affordable if you wish, but bear in mind those cards are expensive for a reason, they're good!
There is some key information to remember however with constructed play, and that is the concept of rotation. Standard is the most popular constructed format, by a very large margin. If someone is playing non-casual magic with their own pre-built decks, chances are they are playing standard. One of the key things about standard is that every six months, usually around late September and early April, several sets of cards are &quot;rotated out&quot; of the format, meaning they are no longer legal for play. this means if you choose badly how you invest, you may well find that in a few months you are no longer allowed to play your expensive cards and have to spend that money all over again. Cards stay in Standard for approximately 15-18 months. On the positive side, this keeps the format feeling new and fresh, however, conversely, it does mean you have to continue to invest in new cards to play.
This puts a lot of people off these formats. Fortunately, there are other constructed formats that do not rotate, however these come with a trade off, as the initial investment is much higher. Eternal formats also tend to have a smaller player base, which means local tournaments are harder to come by, if they happen in your area at all.
Non-rotating formats
Modern - this is the newest and cheapest non-rotating format. This obviously provides a massive advantage, in that cards you buy for this format will not ever rotate out of the format. This means that once you buy a deck - with some caveats - you wont have to make a big investment again. The exceptions to this are bannings, and newly printed cards. If the key elements of your deck are banned (such as Splinter Twin) then you may find you have to invest in an entirely new deck. Similarly, new cards may be printed which become key elements of your deck (such as the new Beck // Call which may well become a core element of modern Elves), however, overall this investment tends to be much more manageable than the continued investment in rotating formats.
Some players dislike modern, and a lot of the complaints raised against it centre around the fact that your investment into the format is not necessarily stable, as if key elements of your deck are banned, you need to reinvest into a new deck. Modern's banlist is relatively young, and as such is still undergoing more change than in other formats. Modern has seen cards banned or unbanned in many of the announcements since the format was officially released. This turbulence puts a lot of players off the format.
Legacy - This is a much more expensive, but also much more stable eternal format, which means that cards from all sets can be played unless they are explicitly banned. The highest value cards in this format are for the most part pretty safe from bannings, as they have been in the format for a long time, and would have been banned a long time ago if they were causing a problem. The main issue with Legacy is that the investment into a deck can easily reach into the region of $1000s. The main advantage is that your investment is unlikely to be invalidated by future card releases or bannings, and for the most part, wont require much (if any) continued investment as additional cards are released.
Legacy has its own problems however, and the prohibitively large cost of the key cards in the format takes its toll, While there are areas with a thriving legacy scene, and even some with higher legacy tournament attendance than any other format, in other areas, the player base is much smaller, and in some areas practically non-existent. Considering the cost of the format, it definitely requires some consideration of your local area to ensure you will be able to play.
Vintage - the most expensive and intense eternal format. This format has a very small ban list (banning only cards such as Contract from Below which reference the &quot;Ante&quot; mechanic which was removed from the game early on, &quot;Dexterity&quot; cards which require you to physically flip cards from a foot above the table such as Chaos Orb, cards with the Conspiracy type like Hymn of the Wilds, and Shahrazad) and a &quot;Restricted&quot; list, of cards which you may only include a single copy in your deck. Some of these cards cost hundreds or thousands of dollars each, and their power level makes them essentially required in your deck. As a result, Vintage tournaments are very hard to come by. I would not recommend going into vintage to someone just starting out.
So, having looked at all your options, here is an overview of what you can expect
Casual play - Comparitively cheap, you can happily play with an investment from anywhere between $20 and $100, depending on how many players you want to support. You can continue to invest to add variety, or play with what you have.
Limited - No initial &quot;hump&quot; of investment to be able to play other than tournament entry, but quite high continued investment.
Constructed
Standard (Rotating) - Reasonable initial investment (approx $50-$500), with similar investment to be made at least every 1-2 years.
Modern (Non-rotating) - Medium to high initial investment (approx $300-$2000), good chance of investment being stable, but good chance you may have to continually invest to keep current.
Legacy (Eternal) - High to very high investment (approx $500-$4000), quite stable investment, continual investment requirements small or non existent.
Vintage (Eternal) - Extremely high investment (approx $4000-$25000) very stable investment, continual investment requirements highly unlikely.