They have even split it into 2 divisions now. The limited class and modified class, and new this year they are trying a truck class. The limited class is highly regulated and even has a "buyout" rule for the A-main winner, which keeps cost down on these cars and modified is just that, the cars are modified and go balls to the wall for the win.
Comparing a demo-derby and bump n run is apples and oranges......demo derby is crashing and hitting and the car last 1 derby unless its like colorado that has a "full-weld" class and these cars do last several derbies but have essentially been reinforced. Bump n run is racing at its finest!
If you scroll up and read other posts, I put the link in for the montana bump n run association which shows pictures of racing and there are even videos on youtube of some races....1 video shows a sweet rollover....but bump n run is just for us wussies out there.