Most racers pay their own way (I sure do). Some of them have some backing from sponsors; often this is the family business. The really good ones get enough from sponsors for this to be their living. Only the absolute top of the top in MotoGP and World Superbike - and not all of the grid, even at that level - are actually paid for doing so. So, during the offseason ... they work their day jobs. When they're not doing that, they're training.
The need for racers to pay for a seat (and it's in the hundreds of thousands of euro per season) in Moto3 and Moto2 has been the subject of controversy; there's a fair argument that it's bad for the sport, and the cutthroat nature of competition is leading to unsafe behaviour on track.
I put together my own bikes, I build my own engines, I've set up my own suspension. Those without enough mechanical ability may be paying for professional engine or suspension work over the off-season.
I've always been my own mechanic and pit crew. Not ideal, but the situation is what it is. Most at a regional level are some combination of that plus friends and relatives hanging out for the weekend. Paying for people to do that ... or paying for multiple mechanics and team members, which is the case at higher levels of competition ... gets really, really expensive really fast.
For the last few years in CSBK, up until now, people were complaining that it was an eastern-Canada series. So, they added a round in Alberta for 2024. Now, they're complaining about the cost to get there and back. Complaining about that is indicative of the shoestring-budget nature of racing in Canada ...
Personally, I'm happy at the moment to be retired from working while not yet retired from (low-level, regional) racing. Means I have time this winter to actually do some training!