I agree with the above. A vanilla 6600 uses regular DDR instead of the DDR3 on the 6600GT on a 128-bit bus, so it's not going to have the RAM bandwidth needed to compete with a 9800Pro and it's 256-bit bus. A 6600GT with ~1GHz DDR3 has what it takes to run with 9800Pro, outpacing it in many situations thanks to the more efficient design of the 6600 series. There are quite a few fanless GF6600s out there, and that may be of interest. However, they won't deliver performance on the level of a 9800Pro or 6600GT.
Budget-wise though, get a 6200 without TurboCache, and with a 128-bit interface. They cost about $60, but they share the same core as the 6600GT's... meaning the core is unlockable, and the memory overclocks well too - though not to 6600GT memory speeds (because they use GDDR3). If you're on a tight budget, that's what I'd get.