You can get modern chips in an AGP card, such as the 6000 and 7000 series (NVIDIA). I have on-board GF4 running Beryl and I consider it very smooth, so I would imagine an FX5200 or better should be great. I'm thinking of getting a $30-40 FX5200, myself. I'd recommend looking around Price Watch
for AGP cards in your price range.