What are you getting for that though?
USAC fees are about $5 per person, plus the permit. (That is for the insurance.) If not USAC, the ride should have some insurance set up.
Are there any police or road closures. Police start at about $35 per hour, and they tell you how many officers and for how long - you don't get to say.
Are there any local permits required? That starts at about $150 per permit. Going through multiple towns or counties may require multiple permits.
T-shirts: figure $10 each
Food and rest stops - your looking at a few dollars per person, at least.
Fuel for vehicles - got to drive that food and water to the rest stations, plus you need vehicles traveling the course for support.
It all adds up very quickly for a promoter. If you've never promoted an event, I highly encourage you to do so. It's an eye-opening experience.