dont go with a low end gpu. it doesnt matter if your cpu bottlenecks a low end card or high end, you will get the same amount of performance. but the benefit of buying a high end gpu in this situation is that when or if you upgrade down the road you dont have that shitty gpu that was giving you the same fps back then but would give you half the fps now.
Aim for a 7750, 7770, 650, 650ti. These cards don't suck a lot of power (less than 100W irrc). We can give more specific advice once you tell us your PSU specs.