I was referring to "modern engines". The Rotax 912 S, 100HP engine
along with the exhaust system, radiator, and other bits costs nearly
$20,000.00. That only leaves you $30,000 for everything else. The
materials for a small, 2 place, all metal airplane from the firewall
back costs nearly $20,000.00 (aluminum is going through the roof
prompting Boeing to switch to carbon for the 787). That only leaves
$10,000.00 for labor and profit. Doesn't look likely to be doable.

Rick