the result is not that great and the price is insane.
It doesn't cost that much to make an engine with a lot of custom parts. Multi axis CNC machining is relatively cheap these days.
IMHO the pricing is insane because all contenders start with a back of a fag packet calculation on how much money they can extract from an FTO doing 500hrs/year, and take it from there. That figure will be £50k to £100k per engine. They are in business, first and foremost.
Lyco sell an IO540 for approx $60k, depending which "cost-plus distributor" you buy it through. The smaller engines cost less. That is your baseline selling price. Obviously nobody would sell a diesel for that, because avtur is cheaper than avgas
If you were to price for the private user you would never bother. And now with tax on private use, the case is totally gone.