CPU+ Mobo: MSI FM2 A75MA-E35 + A6 6400K (183)
RAM: 2X KINGSTON PC 10600/1333MHZ DDR3 CL9 VALUE RAM (2GB) (80)
DVD-RW: LG 24X DVD-RW SATA OEM (25)
PSU: FSP 300W 80% ATX PSU (39)
Case: CM K282 / K350 / K380 (55)
OS: WINDOWS 7 HOME PREM (125)
Total cost: $497
Buy at PC Themes, #04-15, and ask for discounts. DIY yourself. If you can't into DIY, get PC Themes to assemble for you for a fee.
Notes:
1) Due to your very tight budget, an AMD A6 APU based system would suit your needs the best. This is because the HD 8470D iGPU in the AMD APU is roughly equivalent to an entry level R7 240 GPU and is significantly superior to Intel's HD Graphics and thus making this APU a superior choice for light gaming.
2) This systems comes with 2X sticks of 2GB ValueRAMs as the iGPU in AMD APUs work best with RAMs in a dual channel configuration for good performance.