This isn't anywhere under $800 but a great value for gaming thanks to the i5 , SSD , better PSU and better GPU :
PCPartPicker part list:
http://pcpartpicker.com/p/bvVv23
Price breakdown by merchant: http://pcpartpicker.com/p/bvVv23/by_merchant/
CPU: Intel Core i5-4460 3.2GHz Quad-Core Processor ($187.93 @ OutletPC)
Motherboard: Gigabyte GA-B85M-DS3H Micro ATX LGA1150 Motherboard ($66.99 @ Newegg)
Memory: G.Skill Sniper 8GB (2 x 4GB) DDR3-1600 Memory ($69.99 @ Newegg)
Storage: Kingston SSDNow V300 Series 120GB 2.5" Solid State Drive ($59.99 @ Amazon)
Storage: Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive ($53.99 @ Amazon)
Video Card: MSI Radeon R9 280 3GB TWIN FROZR Video Card ($187.27 @ TigerDirect)
Case: Rosewill Galaxy-03 ATX Mid Tower Case ($34.00 @ Newegg)
Power Supply: EVGA 500W 80+ Bronze Certified ATX Power Supply ($47.99 @ NCIX US)
Optical Drive: Lite-On iHDS118-04 DVD/CD Drive ($17.99 @ Newegg)
Operating System: Microsoft Windows 8.1 (OEM) (64-bit) ($101.98 @ Newegg)
Total: $808.12
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2014-10-23 20:31 EDT-0400