I've got about $700 into my current project, but that's not really realistic, considering I got the Phil hubs for a set of NOS campy pista pedals I had in my parts bin + $100, and the saddle, chainring, and pedals also came out of the parts bin.

Bikes can be expensive, and there are some good deals on pre-built bikes out there, but there's nothing like riding something that you built up with exactly the parts you wanted.