I just a few days ago let an OS FP-40 go on ebay. I had the winning bid up to the last few minutes. I had it for $40 NIB. It sold for $57 plus shipping. You can still find deals if you look. And going into winter with the holidays coming the deals will just get better.
There seems to be a good supply of plain bearing motors to be had. And don't turn your nose up at a used engine. Just look at the pictures real close. Look at the exhaust port and see how dark it is. Look and make sure the needle valve is straight and not bent from a crash. Make sure the cylinder doesn't look like a bunch of varnish has been cleaned off of it. Don't forget the Magnum PB ( I can't remember what they are called) engines or the Thunder Tiger GP engines. They are all pretty much copies of the OS engines.
As for buying one of the new OS engines. Yep they are expensive. But you will get an engine you will have a heck of a lot of fun trying to wear out. And they may cost a $150 bucks. But so what? Thats only 2 or 3 tanks of gas in my truck. Take the little wifey out to eat three times and you will have spent that much and all you have to show for it will be in the toilet the next morning.
What was that saying? The quality will be remembered long after the price is forgotten? Something like that.