If you want to race, go to BMW.
If you are set on Pcar, I would suggest SPC. Do a search on Rennlist. I think there were a couple of cars that if still available, could be had in the $40s.
Good Hands got out of GTB before it got too expensive, but he ran both GTB and 99x Cup and would know the cost comparison. I think these days you will need about the same running budget for GTB vs an early Cup. If I were 10 years younger and wanted to race Pcar, 996 Cup would be were I'd go between the two classes.
BUT SERIOUSLY, if you want to race, go to BMW.