I would recommend upgrading your PSU to a non-junk unit first before putting any more money in your system. The last thing most people want is putting in a $200 GPU only to see their PSU make the system go up in smoke.
I'd recommend an NVidia GTX 950 which is good enough for gaming at 1080p in most current games at decent settings. I own and enjoy gaming with my i5-2500k and EVGA GTX 950 FTW. You need to keep an eye on 950 prices because they go on discount often and can be found close to the price of an Nvidia GTX 750ti.
Once you have a NVidia GTX 950 or better your CPU will be the main thing holding you back in gaming.
I would recommend upgrading your PSU to a non-junk unit first before putting any more money in your system. The last thing most people want is putting in a $200 GPU only to see their PSU make the system go up in smoke.
I'm a little tight on cash but what would be a good psu to buy?