None of those racers have much say in how the show is run. That is why big chief quit, he was tired of the bs reality show drama and being told what to do and how to do it.i believe merchandising money which is wholly the teams, is the real bread and butter.
add in the sponsorship deals that could be parts, machine work, clothing as well as the TV money, and possibly contingency money.
as mentioned a lot of them have successful businesses and with that they buy the haulers and cars, put their names on them and now they're a write off thru the business.
i don't know if any of them have any action in the production of the series: producer, created by, technical consultants but if they do, that's real big money.
Remember these guys were racing long before they were on tv and racing lower dollar cars than they are today. They dump all their money into their cars to stay in the top of the game. Some of them have not been able to keep up. Its not always about money, you have to be a savvy racer to go that fast. These cars are in the 3’s in the 1/8 mile.