Buying cheap now or saving for later?
Get something now. Winter is coming…

Seriously though, if you don't have a good feel for what you want in a bike, buying something used that seems close will get you on the road and start you developing the experience you need to decide what you really want.

There are so many variables of fit and gearing that it will be hard to get it right the first time (at least that's been my experience, both with my own bikes and with helping friends and family pick bikes). Add to that commuting and getting back in shape and I think you'd be way better off buying whatever seems best now on craigslist and using it to help you sort out what you really want. A few months into it you'll be in better shape and have some real life experience to guide you in picking your next bike.

Finally there are things you may not have thought of that can make or break a commute – decent lights, riding clothes, a way to carry your gear – that will all add to the cost. Better to spend as little as necessary and have money on hand to add to your kit as you learn what you need to enjoy commuting on your bike.

Wait! There's one more thing… If you buy a relatively decent used bike the value won't change too much over the next 6 months or a year – especially if you take good care of it. So if you decide it isn't the right bike you can get a good portion of what you paid back when you sell it. This will be less true if you get a new bike and then decide to either sell it or start upgrading components.