Here's the link for the Boxster spec racing parts... notice no engine mods... you're in a "race ready" boxster for about 22k to 25k... assuming you buy a used 98/99 to race....
Hardtop mandatory... fire suppression, roll cage, battery tie down highly recommended... billsteins's nice...
http://www.stuttgartperformance.com/ccp/cgi-bin/cp-app.cgi?usr=51F608332&rnd=549593&rrc=N&affl=&cip=&act=&aff=&pg=cat&ref=bsr