http://techreport.com/review/24059/tr-christmas-2012-system-guide/2
i3-3220 ~$130
HD 7770 ~$115
Any Compatible motherboard ~$100
Is your motherboard upgradeable to AM3+? You could keep it and get a new AMD CPU for less than i3+Motherboard.
Alternately if you're just looking for higher resolutions or detail spend only on a $200 graphics card like the 7859 or 650 Ti and skip the new CPU.