I missed the other thread, don't know why it seemed to become a boxing match but...

Here's the answer as I see it. There is something you need to understand. There are two distinct types of gas engines available to us to use for R/C: converts and specifically designed.
Converts consist of a variety of widely available small displacement, 2 stroke, commercial engines - Quadra, Ryobi, Zenoah, Homelite, etc etc etc.... These engines were designed with chainsaws and weedwackers in mind and likewise assembled that way. I have a 24cc Homelite weedwacker that is probably 15 years old. I've NEVER taken care of it yet it starts and runs every time. It's heavy and I'd not trust it on a plane but it runs. To make one of these convert plane-worthy, someone needs to buy them wholesale, do whatever is necessary to make them plane-ready, box them up and market them to a VERY small audience compared to that which buys chainsaws and weedwackers, hence the COGS is pretty significant. I have a converted (albeit used) Ryobi 31cc that is probably worth about $125. It is clear that it is a mass produced unit and new wasn't all that expensive. There is nothing stopping you from buying a $150 weedwacker, stripping all the stuff off it and using the engine in a plane. The conversion really isn't that hard. But you need to consider all that happens to those engines and all the hands that they pass thru to get to the nose of your plane. When Weedwackers-R-Us buys engines, they buy truck loads to make their products with and get a volume price. Horizon doesn't amount to a bit percentage of total sales.
The second kind of gas engine we have available to us are the specifically designed. These engines come from both the US and Europe (and Asia of late) and from the brains of engineers who know modeling. They design these engines knowing full well that not only are they designing for a VERY small market in R/C but a very small percentage of that very small market. BME, DA, 3W, ZDZ, Brison, etc these guys don't count sales in the thousands but in the hundreds. And the amount of engineering, R&D, and manufacturing costs that go into making these little jewels put out the way we expect them to needs to be recouped over a relatively small number of products. And when you compare the output of a G45 or a Q42 with a ZDZ40 or DA50, you'll see a VAST WIDE disparity in power output, weight, and durability. Add to that marketing costs and the COGS is VERY significant. You have the option of buying directly from the manufacturer meaning no middle man (or men). And I don't believe that these guys are getting rich off the sales of these engines. But that is where the cost comes from.

Hope that helps.