Need a little bit more information about the computer you are going to use. Are you building one from scratch, intend to buy pre-assembled or do you have an existing machine that just needs a video card upgrade?
If the later, you do not need a really zippy machine, but make sure the card you buy will fit into a PCI slot you have available.
If buildign your own, you may want to consider just getting graphics processing integrated into the motherboard, and save some coin. The Intel Graphics Media Accelerator (GMA) 4500 scored quite well. Here is a $99 board from NewEgg: http://www.newegg.com/Product/Product.aspx?Item=N82E16813121355&cm_re=Intel_GMA_X4500HD-_-13-121-355-_-Product
If you just want a dedicated GPU to toss into an existing PC:
Newegg has a Radeon 4670 for $65:http://www.newegg.com/Product/Product.aspx?Item=N82E16814161315&cm_re=radeon_4670-_-14-161-315-_-Product
Or you can go for the 5570 at $83:http://www.newegg.com/Product/Product.aspx?Item=N82E16814102874&cm_re=hd_5570-_-14-102-874-_-Product
If you live near a Microcenter, they have an Nvidia 9600 for $45:http://www.microcenter.com/single_product_results.phtml?product_id=0325748