What is the best and cheapest ATI RADEON graphics card to run Call of duty 4?

My graphics card is an Nvidia 8500 and it runs call of duty very very slow, I want to get a new Ati radeon graphics card but which is the cheapest and best for running COD 4?

I would recommend a ATI Radeon 5770. It's about 150 dollars and will run COD4 just fine. Anything lower will probably have FPS problems.

The cheapest radeon at the best price that will run COD4 with good performance would be the ATI Radeon 4850http://www.newegg.com/Product/Product.aspx?Item=N82E16814131163&cm_re=4850-_-14-131-163-_-Product