Usually the prices of computer parts are the same in $ as in £.
In the UK they sell a Powercolour 9700pro for £220.
I know powercolour is not that popular but it seems to be a great card. The fastest of the 9700pros.
http://www.hardocp.com/article.html?art=Mzcz
I dont know a good place in the US to buy it from but it aint too expensive.