If “GAMI’s web site is very quiet on the cost of the STC per airframe/engine combination.” why are we complaining about it?
Let’s say it is $1 a horsepower? That is the same cost of 30 USG of AvGas. So, less than one tank. I’d pay that.
One needs to ask themselves, “How much would you pay to potentially double your TBO?” Because that is the question to ask. Removing lead from our fuel could very well lead to doubling the TBO of our engines, and that is something we will know for certain once we start flying our planes on UL fuel.