I dunno where you live, but if it's near a major metro area (?), I'd suggest going buy a "Bicycle Rescue" co-op or non-profit. They get most of their stock from police departments and other legit municipal donations. Many non-profits can't really handle bikes per se, so they pass them along. Bike Rescues often are staffed with very knowledgeable bike mechanics who donate their time. Most have upwards of a 100 bikes to choose from. They love fitting folks and helping them get into what they want. The goal is assemble a keeper so it won't come through the system again ...

Go look and see if you can find something that really sparks your interest. Often they have bins full of good used parts. A solid chassis will start at $100 or so and they can build it out from there. There are some real high end bikes that get stolen and never claimed (as in from out of town/state) so they are out there. The Police have cleared them of prior ownership. The original owner took the insurance money and bought up. So you can get some nice stuff, and they will make sure it fits you. Take a look ...