Well, I have a good set up that is around 700-760ish dollars. This system does not include os, mouse, or a keyboard. I trust you can find decent ones yourself. You can also pick up windows 7 for around 60-80 bucks these days. My system contains
CPU: Intel Core i5 Processor i5-3470 3.2GHz 5.0GT/s 6MB LGA1155 CPU 77W Quad
PSU: CORSAIR Enthusiast Series TX750M 750W ATX12V v2.31 / EPS12V v2.92 80 PLUS B
GPU: ASUS GTX660-DC2O-2GD5 GeForce GTX 660 2GB 192-bit GDDR5
RAM: Patriot Gamer 2 Series 8GB (2 x 4GB) 240-Pin DDR3 SDRAM
CASE: Fractal Design Core 1000 FD-CA-CORE-1000-USB3-BL Black Steel MicroATX Mid T
MOBO: ASRock H77M LGA1155/ Intel H77/ Quad CrossFireX/ SATA3&USB3.0/ A&V&GbE/ MATX
HDD: NEW Western Digital Caviar Blue WD10EZEX 1 TB 3.5" Internal Hard Drive
DVD: SAMSUNG DVD Burner SATA Model SH-224BB/RSBS
This setup was kind of based off of Jackfrags' video on a simple 300 pound computer that can run games well. But the computer can run games alot better, if some components are not compatible, don't be afraid to ask around and try to find a better item. Mainly say that because the ram is out of stock from the company, so search around newegg or ebay. Hope this system helps you!