I'm gonna try to make a very objective post, hopefully this will not turn into a flame fest...
Your best bargain is to buy something used from the For Sale/Trade forum right here. Radeon 9700 or better, basically something with 256 bit memory and 8 pipes. I would look to spend around $200.
Should you want to only consider 'new' cards, and I am in no way insulting your judgement on that, I would recommend getting the cheapest 9600 Pro (Or XT) you can. Ideally around $150. Reason being the 9600 Pro/XT is fast enough to run every game on the market at a decent resolution and framerate. By the time D3 and HL2 come out, you'll be able to buy better cards than the 9800 Pro for half the money.