R9 270X is around ~$200 and should do the job.
(http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&DEPA=0&Order=BESTMATCH&Description=R9+270x&N=-1&isNodeId=1)
If you have the budget and somehow plans to buy a better monitor in the near future, get a GTX770 or R9 280X.