If you want to compete, and you're not in the 1%, then build (or work towards building) a spec Boxster. This uses the 986 car (1997-1999), the base 2.5 liter engine. It's by far the most popular PCA racing class. Also legal with the SCCA (class T3) and NASA. You can pick one up for a few thousand dollars. And then spend another $25k making it into a race car. Here's a
spreadsheet of parts and costs.
PCA rules are
here. Look at the SPB rules starting on page 24.
Fellow Spec Boxster racers hang out here and also
on rennlist.
I suggest going to some PCA races in your region and meeting some fellow Spec Boxster racers. They're generally a pretty friendly group.