I just made mine up:
$30 - complete (but dodgy) ebay bike
&250 - wheelset
$80 - cog, lockring, tyres, tubes
$10 - bartape
$100 - cranks and chainring
$30 - Cartridge bottom bracket
recycled bars, stem, frame, fork, pedals, front brake and lever

$500 all up. It's a bit much, but that's in australian dollars, so it's a bit less than it seems

and to the person who said that you shouldn't do this unless you're experienced, i'd strongly disagree. I've found this to be the best learning experience, and I could have done it even if I hadn't had experience installing and adjusting derailleurs and all that stuff.