$20K is on the very high end for this MY.
For a PPI in the Plano/Frisco area, you could contact Danny Kehah at Fix N Go. Don't let the name of the garage fool you, Danny is a Gold Master Certified Porsche technician, and he can provide a PPI to your specification. Just depends on how deep you want to go with the inspection. Leakdown test, oil change, etc.
Porsche Repair by Fix N Go in Plano, TX | PCarShops.com
BTW, please be aware that the 2002 - 2005 Boxster engine has the single row IMS bearing with the highest catastrophic engine failure rate.
Just sayin'...........
TO