For $150 you can get a 650ti or if there is a sale, even a 7850. Unfortunately your power supply can't handle either. So you should upgrade that psu before you buy a graphics card. With that cpu you may want to overclock or purchase a lower end card just to prevent bottlenecking.
If OP has already upgraded to a CX 500, then OP should be fine with a Radeon 7850 or a GTX 650 Ti. I wouldn't go much farther in upgrades with that PSU unless it's a V3 model, but it should be fine with OP's current system and up to a Radeon 7870 or so for graphics (granted that would be out of OP's budget).