Well if if its a fight between Nvidia and ATI at the price point you are speaking of. you can easily get carried away and bump for 48dollar budget to 110dollars... Yes you will get that much better of a card.
If your goign between a gt 430, 240, 620. Its all in the same ballpark.
ATI you will get perhaps slightly better performance for the money, but am bias to Nvidia due to the driver support and alot of games really take advantage of their technologies.
So fanboys of ati and nvidia will direct you to their side sure.. but if you are looking for a certain price for performance, stick to that. and it should be clear. Just make sure you get a recognized brand and stay away from refurbish products..