I bought a running O-320-E3D for $3500, bolted it on and flew for 3 years. When I tore it down for rebuild, it was still running great at over 2800 hrs. and all parts still met tolerance. I only rebuilt it to increase HP.
I bought one off of a local bird that was damaged in a tornado DURING the annual inspection but after the engine was done. Running strong at 1600 hrs for $5K.