KiritoPCPartPicker part list / Price breakdown by merchant / Benchmarks
CPU: AMD FX-6300 3.5GHz 6-Core Processor ($109.99 @ Amazon)
CPU Cooler: Cooler Master Hyper 212 Plus 76.8 CFM Sleeve Bearing CPU Cooler ($28.97 @ Outlet PC)
Motherboard: Asus M5A97 LE R2.0 ATX AM3+ Motherboard ($64.99 @ Newegg)
Memory: Corsair Vengeance 8GB (2 x 4GB) DDR3-1600 Memory ($63.99 @ Newegg)
Storage: Western Digital Caviar Blue 1TB 3.5" 7200RPM Internal Hard Drive ($59.98 @ Outlet PC)
Video Card: Asus GeForce GTX 650 Ti Boost 2GB Video Card ($168.98 @ Newegg)
Case: Fractal Design Arc Midi R2 (Black) ATX Mid Tower Case ($59.99 @ Microcenter)
Power Supply: Corsair Builder 500W 80 PLUS Certified ATX12V Power Supply ($29.99 @ Newegg)
Optical Drive: Samsung SH-224BB DVD/CD Writer ($29.94 @ Adorama)
Total: $616.82
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2013-08-28 20:08 EDT-0400)
Here's a build I made if you've decided to start by scratch. You can easily torrent Windows 7 and put it on a usb drive.
a 7870 is around the price of the 650 ti boost and a bit better