A good budget gpu is the Evga 9800GT. It can run almost anygame maxed out. I think its only $120.
see heres the deal, just because you have the budget for the best components on the market doesn't mean thats the best price/performance.
if you just want the best computer you can build with your current budget then grab it up but if you're looking for best price/performance components then its best to search google and get a general professional census on that point