Keep it simple, keep it reliable.

Stock Recaro seats - Check!
Oil pan protection - Check!
No nerf bars - Bummer!
14" stock wheels - Check!
CHEAP 14" tires - Check!!!

Barry, I don't think you should even bear the brunt of the cost for the cars. All of your drivers are going out to have fun and abuse your equipment. With 14 drivers, add another $50 to their "prep fee" to help cover that. Trust me, there are going to be enough incidental expenses that will creep up... get money where you reasonably can!