What is "affordable" exactly? Bill Gates has a very large "affordable" range while a kid off the streets of Bolivia would view "affordable" a bit differently.
Also need to know your case model and power supply brand and model and wattage.
For that resolution, you would probably need a mid-range card in the high $100s low $200s. Look here: http://www.tomshardware.com/reviews/gaming-graphics-card-review,3107.html