In the early naughties i found a Giant AC1 in the trading post almost complete in really good nick. $800, included, frame with shock, forks, wheels, bars, seat, seat post, headset. (Included the 3 most expensive bits, frame, fork and wheels.)
All I needed to source was
- Grips
- Brakes
- Cranks
- Pedals
- Derailleurs
- shifters
- chain.
I sourced bits from all over the place, took my time to get good gear at good prices, and generally got good deals. The bike complete ended up costing me about $2,200.
If you only have a frame at the moment you are going to need to source everything else separately which is either going to cost a fair bit, take a long time, or be shit gear (similar to the pick any 2 of the 3 principal). You could get lucky though, depends on the market at the time you are looking.
I would recommend buying a complete bike second hand. The more stuff you sorce from the one location/person the better the deal you should get.