Consider how you're going to ride the bike...If you're going to be on asphalt a road bike might be more efficient, but if you're going to be on other less regular surfaces, you may want something that was built for rough terrain.

Do you live in an area with an active Craigslist site? Because that would honestly be my first suggestion. If you're willing to hold off on buying for two weeks and comb the Craigslist site daily, you will likely find a quality used bike that could last you longer than most new bikes from a big box store.

On the other hand, my ride is a target-issue Schwinn hybrid that I paid $200 for. I like it a lot and it suits my needs, but there are definitely some things about it that I'm not in love with, particularly, its weight and the (cheap) grip-shift system.

But by and large, any bike will do the job.