No idea... I think it's the same from '69-'71, but I'm not that sure on truck stuff. I don't know how subject to damage they were, which is usually a good indicator of how expensive they've become.
If he eBays it, have him make sure to insert the word "Dude" somewhere in the auction as a keyword... the "Dude" models have quite a following among old Dodge truck fans, potheads, and fans of The Big Lebowski.