An i3-2100 would be a better gaming CPU despite only 2 cores. It's usually cheaper too. Here's the cheapest gaming build I've been able to come up with, should be ok at low resolutions.
Antec EarthWatts Green EA-380D 380W
MSI HD 5670
4GB G.Skill NS
That comes to $350 on Newegg. It would really benefit from spending an extra $50-100 on the graphics but as i said, HD 5670 is ok at low resolutions.