I guess if you include the cost of bikes, entry fees, camping permit, etc for the 1410 riders that are entered into the Loretta Lynn's final, each rider will have $10,000 wrapped up in their racing for the year. But that doesn't all go to MX Sports, the biggest chunk of it would go to the bike purchase and then many costs going here and there after that to get in.
MX Sports gets
$10 - Area Qualifier Fee from approx 18,000 racers = $180,000
$40 - Regional Fee from approx 7 regions regional registration fee for 36 classes (64 max riders per class) = Max of $92,160 if every class had 64 riders at regional
$305 - Loretta Lynn's facility permits times 900 racers (some racers ride 2 classes and only pay once of 1410 entries) = $274,500
$75 - Class fee times 1410 entries = $105,750
$25 - Pit vehicle fee x 2000 pit vehicles at Lorettas = $50,000
So MxSports brings in a maximum of $702,410 from the racers that go through the process in some form or another (that is exaggerated as most classes are not full at regional and paid $40 in full capacity).
Of course, it's a business and they are making money, but putting on the show, running the equipment, paying all of those workers, and renting Loretta Lynn's campground can't be a cheap endeavor either. But that gives you a realistic idea of what type of money is going through MX Sports hands on the process of Loretta Lynns.