The guy wants $5000 for it.
Funny, he mentioned he was wanting to downgrade since the CBT was way too big for what he needs (scraping the driveway and plowing snow). So now we're talking about swapping out even for my Satoh s650g. The owner of the CBT said the service guy he talked to was going to charge ~$600 for the rebuild/cleanout. It has other minor things that need work too: right brake is leaking fluid, lights need looked at, but I'm told that the engine is in great mechanical shape.
I talked to a couple of guys around here and they said $600 sounds about right.