The 9500 is certainly a better deal if you don't mind the hassle of a rebate, but the 4650 is more powerful by a significant margin.
The 9600 GSO should be a bit better than an HD 4650, but with shipping it comes out to $72 - $30 rebate = $42. Probably the best <$50 card you can find, but if you don't like rebates then the price is pretty high compared to your other options.
Also if you're really not worried about games, the 9500 GT should be just fine. It'll require the least amount of power too.