RE: Why the big price difference??
The manufacturers make the price what they can.
Repeat customers and reputation seem to be the reason some are way more expensive than others. OS for example makes over a quarter of a million motors a year. And sells them at the prices they ask. Reputation?
McCoy used to sell engines at about half the price of similar sized OS engines back in the 70s. If you figured out how to run the McCoys and not burn 'em up, they were a heck of a deal. OS is still doing what they did back then. If Magnum keeps making good engines, they might be around in 30 years too.