Have you taken pictures for this type of series before? If so, this would be my suggestion to you:
I would figure out how much time you spend at each race, editing photos, driving time etc. Then, get an idea of what you want to make from this (i.e. hourly wage). It could either be for the season as a whole or on a per race basis. Simply present your figures to whom ever suggested they were going to hire you and see what they say.
If you have taken pictures for them before (or have seen your work elsewhere), and they really like the photos, they will be more likely to agree to your prices. You could also offer custom cd's for purchase of the drivers.
I mainly shoot high school soccer and football, so I'm not sure of pricing for racing. For myself, I usually try to get at least $50 per game plus I sell photo cd's and some custom posters. That's a little on the low end, but I'm just starting out also.
So far, everyone seems happy with what I've done for them (knocks on wood...).
The pricing for you could be higher depending on a few things, hopefully some others will add helpful input.