I recommend to get the FX cpu, because it is a newer socket type AM3+ and athlon is FM2 socket, which is harder upgrade in the future. I add other list too, and I recommend to get the better GPU like the r7 265 I think the price will be in your budget range.
The MB GA 970 A ud3p has 8+2 VRM, that you can use it with other fx cpu up to FX 8 seiers.
So you can pick the components by cherry-pick from the list.
PCPartPicker part list:
http://pcpartpicker.com/p/3AQBd
Price breakdown by merchant: http://pcpartpicker.com/p/3AQBd/by_merchant/
Benchmarks: http://pcpartpicker.com/p/3AQBd/benchmarks/
CPU: AMD FX-4300 3.8GHz Quad-Core Processor ($109.99 @ Newegg)
Motherboard: Gigabyte GA-970A-UD3P ATX AM3+ Motherboard ($79.99 @ Newegg)
Memory: G.Skill Ripjaws Series 8GB (2 x 4GB) DDR3-1600 Memory ($74.99 @ Newegg)
Storage: Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive ($54.99 @ Amazon)
Video Card: MSI Radeon R7 265 2GB Video Card ($149.99 @ Amazon)
Case: Cougar Solution (Black) ATX Mid Tower Case ($34.99 @ Newegg)
Power Supply: EVGA 500W 80+ Bronze Certified ATX Power Supply ($39.99 @ Newegg)
Total: $529.93
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2014-04-29 16:43 EDT-0400)