That is a low budget. A HD 7770 is probably the best bet. Though, I would recommend a GTX 650 Ti Boost if you can afford it. In SLI, it achieves very high results, being on par with a GTX 680.
That's kind of low. Both your CPU + GPU will use up 205W. Then you have your RAM, HDD, and Motherboard. It's definitely cutting it close. You probably won't make any good use of your GPU unless you want to crash your system.