Ah ha! If you don't know what you're looking at, get a used bike from a local bike shop! A lot of them sell used bikes. It's what I did, and I know I got way more for my money than if I had bought a walmart special : / the mechanics would never sell a bike that wasn't safe, but look up reviews for the shop before you go just to check them out. Either way, you don't really have anything to loose by dropping by and taking a few test rides (it did take me a while to find my perfect used bike, I went to 4 different bike shops before cupids arrow hit me).

Plus, vintage steel bikes are sooooo stylish!