From what I've seen, the late model rollers usually go straight from the bike shop who have quoted $3000 for a rebuild, directly to the wrecker.
Virtually every wrecker seems to have at least one newish 4-stroke MXer with the motor in a box, but they always part the bikes out....
FWIW, I missed out on an '06 YZ125 with a seized bottom end and a melted fuel tank for $1000 the other week. The melted fuel tank (and CDI box) bit was a bit scary, but without seeing the bike, I don't know how scary.
There's an 04(?) KTM 4-stroke with a dead motor that's advertised locally for $2300ono, if that means anything.