What should you expect to pay for a used (currently running in an airframe)? Or, what should you expect to get if you are selling the same? What is the realistic market?

Reason is: I'm considering a new engine to replace my 1600 hour+ 912ULS (currently flying & running well. I recently have seen a Barnstormer ad asking over $10k for a 1500 hour ULS and another EBay listing asking $21K for a 37 hour TT ULS. Both of these examples seem way over-priced since a brand new one is $18,500+.

In the recent Rotax course I took it was pointed out there are very few engines being overhauled. Most operators buy new and improved engines.

Opinions or info anyone?

Thanks much,

Skot
Vixen N24V
912 ULS, Ivo