Upgrading Inspiron 620 GPU mid tower

Hi fellas, I am the lucky owner of a Mid tower Inspiron 620, my PSU was upgraded to 450W. I am now looking to get a good GPU that could run StarCraft 2 at high settings, I am looking for something at maximum 200 dollar CAD. Here are the specs of my machine Intel core i5-2320 3.00GHz 3.00 GHz, 6 G of ram (willing to bump* the ram if needed). I am running Windows 10. Thanks for the support  :D

Christian