Considering that you can probably reuse at least your HDD and your GPU, here's my recommendation on the other parts :
PCPartPicker part list:
http://pcpartpicker.com/p/1zxzx
Price breakdown by merchant: http://pcpartpicker.com/p/1zxzx/by_merchant/
Benchmarks: http://pcpartpicker.com/p/1zxzx/benchmarks/
CPU: AMD FX-8320 3.5GHz 8-Core Processor ($144.99 @ Amazon)
CPU Cooler: Cooler Master Hyper 212 EVO 82.9 CFM Sleeve Bearing CPU Cooler ($34.99 @ Amazon)
Motherboard: Asus M5A97 R2.0 ATX AM3+ Motherboard ($95.99 @ NCIX US)
Memory: G.Skill Sniper 8GB (2 x 4GB) DDR3-1600 Memory ($58.50 @ Newegg)
Case: Corsair 300R ATX Mid Tower Case ($49.99 @ Newegg)
Power Supply: XFX 550W 80 PLUS Bronze Certified ATX12V / EPS12V Power Supply ($61.24 @ Amazon)
Optical Drive: LG GH24NS95 DVD/CD Writer ($19.99 @ Newegg)
Total: $465.69
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2013-09-03 11:42 EDT-0400)