If only $150 to spend, then there's not much reason not to buy a 9800SE w/ 256-bit memory interface (R98SE-C3). It has everything the 9800 Pro has, except for lower-quality memory and half-of-eight pixel-pipelines disabled. A Radeon 9800 Pro costs ~$50-60 more then a PowerColor R98SE-C3.
Compared to a 9600XT, a PowerColor R98SE-C3 has a leg-up in every aspect except memory usage. But high memory clocks arn't worth a damn if you lack half of the 256-bit memory interface found on the 9800 Pro and PowerColor R98SE-C3.
Radeon 9800 Pro - $210-220
Memory Interface: 256-bit
Memory: Samsung/Hynix 2.86ns
Core: R350
PowerColor R98SE-C3 - $160
Memory Interface: 256-bit
Memory: Infineon 3.0ns
Core: R350
Radeon 9600XT - $150-180
Memory Interface: 128-bit
Memory: Samsung 3.3ns/2.86ns
Core: RV-360