Race entry fees run $225-300 with NASA. Including entry fees, tires, and other things you can certainly race for $5,000 - $10,000 per year including all fees and travel expenses, especially if you plan to handle most of the maintenance work yourself. Except for crash repairs, the top teams are probably spending about $15,000 per year and some of that includes testing and a lot of travel.
Costs are a big advantage to the cars: maintenance and parts tend to be relatively inexpensive and last very well. Running with Factory Five is one of the least expensive ways to race.
CREDIT: Dan Elam