How much does it effectively cost to purchase currency at an exchange? If I buy crypto-currency at, for example, Kraken, how much does it effectively cost me to buy it and move it to another wallet or exchange?
Essentially, you have to factor in 3 fees in a purchase:

1. Deposit fee (if applicable)

This is usually a fee for wire transfers, and from my experience is only relevant if you deposit cash across economic zones, albeit this is slowly reducing to 'anywhere to asia', or outside of the SEPA zone. 

Kraken charges 5€ per wire transfer, SEPA transfers are free as of the time of writing this post.

2. Trade fee

This fee depends on 2 factors:


Your current trade volume tier, which you can find at the top right of your account on the Kraken webpage. This is calculated in fiat currency, and based on the traded volume in the past 30 days.
The order type you buy your currency with. A Taker fee is charged, if you buy using 'market' orders - that means you'll get the best available price on the market for the volume of currency you'd like to buy/sell. 
If you buy using any other order type, you'll be charged the maker fee. You'll notice that the taker fee is higher than the maker fee - this is because it is assumed that buying via market orders takes away liquidity from the market (there are less offers available), whereas limit and other order types add liquidity to the market (it adds to the offers available on the market).* 


*It is worth noting that some exchanges still charge you the taker fee, despite quoting using limit orders - this usually happens if you quote an existing order, causing your order to resolve instantly. Bitstamp is such one example. After checking back with Kraken, this is also the case at Kraken.com.

3. Withdrawal Fee (if applicable)

This fee is charged with any withdrawal you make from your account. On Kraken, this fee is 0.0005 BTC for BitCoin, and 0.02 LTC for LiteCoin withdrawals. Additional fees are charged if you use BitGo, which adds an additional 0.1% cost to your withdrawal. In cases where you may need your BitCoins fast, this may be worth it. You can check on the fees for other currency on their respective withdrawal page on your Kraken Account's website under the Funding tab.

Bringing it all together

This put all together leaves you with the following (slightly unwieldy) formula to calculate your actual cost of purchasing currency at Kraken:

(Deposit Fee) + (Order Volume * Quote Price) + ((Order Volume * Quote Price) * Transaction Fee) + (Withdrawal Fee * Quote Price)


Please keep in mind that your bank and any recipient you send your currency to may also charge you fees; these will have to be factored in as well.

Trade safe!

Example: 

You'd like to buy 1 Bitcoin @ 500€, deposit via bankwire, use a market order and transfer it via BitGo Instant. Your Trade Volume Tier is 1.

Deposit Fee = 5€

Order Volume = 1

Quote Price = 500€

Transaction Fee = 0.0026 (or 0.26%)

Withdrawal Fee = (0.0005BTC + (Order Volume * 0.001)) * Quote Price

Gives you this:

(5€) + (500€ * 1) +  ((500€ * 1) * 0.0026) + ((0.0005 + 0.001 * 1)) * 500€) = 507.05 €