As far as permit cost, they only care about people. Driver and passenger cost the same. When I was doing the permitting, the BLM asked for a vehicle count for their record keeping, but it had no influence on the permit cost.
This is somethin a lot of people misunderstood about the permit requirement and was why a lot of events got letters from the BLM letting them know they were in violation and needed a permit for their event. They thought, "Hey we only had 20 rigs on the trail and the permit says 25." But it's 25 PEOPLE. So with 15 to 20 rigs it's easy to get over the 25 people limit.