First Time Building- Need Cheap Gaming Comp.

Ok, so i've recently discovered the hatred for the pre-built computers of Dell and HP after mine crapped out on me for trying to upgrade the GPU and PSU, that said, i found this website, and witnessed the high level of IT knowledge it's citizens have. So, i've done some research, and concluded that i should just ask, and see what i get.

SO, here's the gist of it; I want to build a PC for near $700 dollars and i want the ability to upgrade it later on, and by that i mean the CPU and other key components, so that i don't get left behind in the ever advancing world of computer technology.

Its gotta be able to play WoW on high-ultra settings, and be able to play Crysis and Rift on medium or so settings.

Sounds like i'm asking the world? Nah. i just want the best i can get, for a low price (with later improvements).