$350 for mobo, video card, PSU, RAM, and processor. I can give you the exact list of stuff I got from new egg. I can max out crysis with 2x AA and get ~37FPS
That's actually slightly different, because they no longer sold the powersupply, but that's a better one for less anyhow. After the mail in rebates, that should be really cheap, and all you have to add is the case, HDD's, and optical drives.