You should buy a decent Lenovo or Dell/Alienware of off Offerup, you'll come in with the deals.
I got myself one for $400 with 2.4 Ghz i7 Quad, 24GB DDR5 ram, 2GB DDR5 GeForce 7 something, and it has everything you'll ever need on it (ethernet, 5 usb ports, etc.).