Last summer, I managed to find a Gitane Performance bike in excellent shape out of the dump. Restored it and built it up for a coworker for about $150. When I pulled it out of hte dump, it had some pretty low-end components; suntour shifters & derailleurs, and no brakes, and the wheels were actually non-existant. Ended up using a donor bike pulled out of the same dump to provide some Sora indexed brake shifters, and sold off the parts I wasn't going to use from both bikes, to fund buying some new stuff.

Final build:
Gitane frame & fork, w/ donated seat & no-name AL handlebars, and a TTT stem. Alex wheelset - $20. Truvativ triple crankset - pulled from donor bike. Shimano BB - $20. Tiagra derailleurs, $80, tiagra 9-speed cassette, $35. Tektro brakes - from donor bike. New cables & housings - $25. Tektro brake levers - from donor bike.

All told, I think she ended up spending less than $140 out-of-pocket, and the remainder of the cost was covered by selling off the unused parts. And I got to build my first bike from the ground up. Learned a lot with that build.