I wouldnt call a 100hp (Rotax 912) or 160 hp Lycoming high performance as far as horse power and torque goes. When you talk about $10,000 car engines your talking about alot more HP then what is used in the avg RV world.
I have a friend who built a Factory Five kit car with a 500 HP Chevy crete motor. I think he paid around $14,000 for it ready to run with fuel injection and all. He has 40,000 miles on his car and it hasnt missed a beat yet. I can only guess what a fuel injected 500 HP Lycoming would cost
I think it all boils down to a combo of 4 things:
1)
Number produced (R&D / Tooling cost)
2)
Lawyers
3)
Higher labor cost(I was into skateboarding in the 80's and a high end skateboard was $100 complete in 1987. I just bought my daughter a high end one last week that was $80 complete. That means that your getting better / newer technology at a negitive inflation rate which is amazing

) But then again skateboards are made in China along with most other stuff and if airplane engines are built in the US or Europe then the labor cost have to be alot higher.
4)
Govt. Regulation (sometimes good, but when was the last time the Govt turned anything into an easier / cheaper thing)
I think that pretty much sums up the why part.
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