I already got the thing and some upgrades from the storeroom at work. So far I am looking at:

Geforce 9400
4gb ddr2 800
1 320 gig and one 160gb hard drive (both 3gb/s sata)
Athlon X2 6000+ 3.1ghz

and I have only put about 250$ into it.

It will go to about 350$ if and when I decide to upgrade to the 9800gt, and I might spring for a snazzier processor. (I found out that the socket AM2+ chips might work on my motherboard)