Most will charge by the job. Those race guys wants very specific, highly detailed stuff.
If the printer makes the art available in more than just screenprint form i.e. poster art etc.
then the racer should be willing to pay $300 - $900 for art thay can repurpose for calendars, frisbees, posters, mugs, etc.
The client is paying for art they can use for the full season.....shirts are just part of it.