OK.........Not quite what i was after.
As Ash has stated, a format of events, etc. would be of greater help. If it's a track day, just mention that cars will be released in groups of X cars, for Y laps, or Z minutes. Is the long or short track being used?
From the sound of it, looks like you have booked the track, but have not planned and events or what you plan to do on the day.
Does this mean if you get 10 people, you expect them to pay $615 each to cover your costs? A set price would also be better; obviously the lower the price the more people will come.Go back to the "drawing board", nut out all the details, including entry price, then post up all the information.