Here is a build well under 500$, you will have to take advantage the G3258+ Z97 PC Mate ($100, and a 10$ rebate is available) from your local Microcenter and the gpu can be purchased from gpuShack using the promo code "EMAIL10" which will drop the price to 139$ for an HIS 7950 Boost.
I went with 1x4GB of RAM because you can easily upgrade in the future and add another stick of 4GB to use dual channel in the future for 8GB total.
The G3258 is an excellent cpu for budget gaming/overclocking monster and slightly outperforms and i3 4160 in terms of single core performance and the Msi z97 Pc Mate is an excellent motherboard which will allow you to upgrade to a new Haswell architecture cpu in the future if you decide to like the i5-4690k
The HIS 7950 boost is highly comparable with an R9 280 and the website, gpuShack, sells refurbished gpus but don't let that scare you, their gpus run flawlessly and I've never had any problems with the one I own (R9 280x) and the 2 others that my friend purchased.
PCPartPicker part list / Price breakdown by merchant
| Type | Item | Price |
|---|---|---|
| CPU | Intel Pentium G3258 3.2GHz Dual-Core Processor | $50.00 |
| Motherboard | MSI Z97 PC MATE ATX LGA1150 Motherboard | $50.00 |
| Memory | G.Skill Ripjaws X Series 4GB (1 x 4GB) DDR3-1600 Memory | $32.98 @ OutletPC |
| Storage | Western Digital Caviar Blue 1TB 3.5" 7200RPM Internal Hard Drive | $44.99 @ Best Buy |
| Video Card | HIS Radeon HD 7950 3GB Video Card | $139.00 |
| Case | Corsair 200R ATX Mid Tower Case | $49.99 @ Amazon |
| Power Supply | EVGA 600B 600W 80+ Bronze Certified ATX Power Supply | $44.99 @ NCIX US |
| Prices include shipping, taxes, rebates, and discounts | ||
| Total | $411.95 | |
| Generated by PCPartPicker 2015-03-09 16:39 EDT-0400 |