Here's the update.

Competitor vehicles = 4 (Ben, Antz, Pavlo, Jason)
Includes spectators (Ann, Pavlo's Brother, Jason Spectator 1, Antz spectator 1)

Additional drivers = 0 (noone's driving anyone elses rig AFAIK)

Additional non driving adults = 6 (Chris, Brad, Jason Spectator 2, Antz spectator 2, Bill, Sylvia)

Dinner on Saturday night = 12 (Everyone except Bill & Sylvia)

Event Polo shirts = 3 (Ben, Pavlo, Brad. Let me know who else and what size ASAP)

That brings it to a total of $539