I bought a near new 2001 KX500, the KX500AF was an after thought. I saved $4000 supplying an engine to AJ for my Service Kawasaki KX500AF. He has never let anyone supply a donor engine for a build and most likely won't let anyone supply an engine again. My engine was near new, that's the only reason he let me supply it. It's hard for them to keep their hands on quality control when they install a used engine. I have an understanding with AJ/Service Honda, there will be NO complaints on how my bike performs. That's totally on ME. I have total confidence with my engine in their bike. They made sure everything worked on their end. Engine was up to me.
With shipping of the engine, cost of my used bike and the cost of the new KX450F, I still paid $11,000 for my KX500AF. The only difference, I have a rolling chassis, less engine and engine components.
My build,
http://www.kxriders.com/forums/index.php/topic,4784.45.htmlI have no idea on where to buy a "good" engine. E-Bay is a crap shoot. It's like a box of chocolate, ya never know what your going to get. Ask all the right questions and make them supply lots of pictures. Get a shot of the piston through the exhaust port.