your best bet would be to build one honestly. mine was built for 400 dollars and it runs the game with all the setting on as high as possible. just look up how to build one if you dont know how, its easier than it sounds:D
Edit:http://www.newegg.com/Product/Product.aspx?Item=N82E16883113175
that should run it perfectly
look around on http://www.newegg.com they got good deals.