Depending on where you live, you could look for the GDDR3
versions of the 7300GT from either Inno3D
. These cards appear to overclock to almost match a reference 7600GS according to the reviews I've read. They're more expensive than standard GDDR2 7300GTs, but usually come in cheaper than the reference 7600GSs.
Unfortunately, if you're located in the U.S., good luck finding them.
Instead of looking for the new low-budget cards, you might want to try looking for older mid-high end cards from the ATI X#00 or nVidia 6#00 series. Ebay would be a good place to start. You might get luck and find a decent X800 series card with a 256-Bit memory interface in your price range.