Here's a very rough outline for used, good quality, parts:
Bottom Bracket - $30
Crank w/chainring - $40
Pedals - $20
Wheelset including tubes/tape/tires - $150 (this can vary greatly)
Cog and lockring - $30
Stem - $15
Bars - $20
Seatpost - $15
Saddle - $20
Brake lever (if you want one) - $10
Brake Calliper (if you want one) - $20
Misc (like bar tape, bottle cage, etc.) - $20
These are rough guesses for quality used parts. A lot these prices are more near the bottom end than the top end. If you look around quite a bit, you can get stuff for next to nothing. Takes time though. Just depends on how much work you want to put into it.
Oh yeah, those prices don't include labor at the LBS or tools/time on your part.