You could loose another 100-125 on chip... a chip a bit lower, will almost have no effect on gaming. these days, EVERYTHING is all about the vid card.. the chip just calculates AI, and these days, any 4 year old chip will handel what game companies are doing. My intell 8400 is going on 5 years old, and has no problems. You can get a chip that is 2-3 years newer, for under 100 bucks.
Case/ps you can also save a little money if you want..
Basically, what you do is make the computer with a couple planed upgrades.. You get a good board, with a low end chip, but make sure the board can handel the better chip.. then when those good chips that are 400 bucks drop to 70 bucks in a couple years, you pop it in with a new vid card, and poof brand new system, for about 200 bucks 2-3 years down the road.
Basically if you have to buy the OS, you should beable to fund something for about 600 bucks, shipping included, from
www.newegg.com. All parts you buy will or should have a 3 year factory warrenty.. which is typically a year longer than most computer manufaturers pre-built