[Bags]

CD Drive - $15
Case - Rosewill CHALLENGER Black Gaming ATX Mid Tower Computer Case - $50
Hard Drive - Seagate Barracuda ST250DM000 250GB 7200 RPM - $70
Video Card - EVGA 01G-P3-1361-KR GeForce GTX 460 (Fermi) 1GB 192-bit - $115 after $25 MIR
RAM - G.SKILL Value 4GB 240-Pin DDR3 SDRAM DDR3 1333 - $20
Motherboard - ASRock H61M/U3S3 LGA 1155 Intel H61 - $67
CPU - Intel Core i3-2120 Sandy Bridge 3.3GHz LGA 1155 - $125

Total - $496 including shipping.

So around ~$500 if you can reuse the powersupply and the OS. Given a 1280x1024 resolution, should do most games out now on medium with good fps. What is the powersupply's model?

Anyway, come back again when you have the money, you'll probably be able to get more for your money then.