We have something similar in Norway, but shorter races on rally cross tracks. To keep drivers spending and tuning in check, the winners car is offered for sale at ~500$ after the race.

Have the price for the cars dropped? When I was racing in bilcross ~15 years ago the price for a car was 9000 NOK. You can also bid on any car that have been in the race, not only the winners and you cannot refuse to sell. Personal safety equipment is not part of the sale. Bid is a fixed price and if several bids on the same car they draw one of the bids on random. It is tons of fun racing and safe even if you get in a heat with many who have never raced before

Sweden and Finland do also have the same, is called folkrace there

Sorry, meant to write 1500$ (or 15.000 NOK) which I believe is the current bid price. I never raced myself, but it does sound like great fun!

There's a similar mechanism for most horse races in the US, though instead of it being just the winner's entry, all of the horses in the race are offered for sale at a certain "claiming" price just before the race starts.

https://en.m.wikipedia.org/wiki/Claiming_race

In the USA they have had similar rules for some motorcycle racing classes to make them more even. Sometimes a super trick bike with lots of trick factory parts gets bought for pennies on the dollar.

I did not know about that. What's the name of those races? How can I find out more?

Folkrace! Kills me that it's not a thing in the US. https://en.wikipedia.org/wiki/Folkrace