I built one offa newegg for less than 300 bucks. Right after Christmas, rehashing and rehashing combo deals/coupons/shipping deals. It was a pain in the ass to design but totally possible. It obviously isn't a powerhouse but it's running Shogun 2 and Crysis 2 just fine.

You can cut a lot of costs if you're not totally ignorant. Doing simple math of multiplying by 10 and generalizing or going to Best Buy and seeing what they have on the shelf there for two grand isn't gonna cut it.