If all you looked at was the asking prices you are only getting half the story. You need to run the auction numbers as well. Pick a 2004 D8RII and run the search for the last year. Run either the asking or the auction numbers. When you get to the result page look in the middle top of the page and you will see a field that says "view high low average." Click on that field and you will come up with three sold at auction averaging $82,833 and one asking price of $102,000. That's about a twenty percent difference. You know all dealers are going to put a thirty percent markup on their costs to obtain and prep the machine. You also know the average auction number is going to have costs as well so maybe you figure the actual seller only got $74,550 or less. Now you have a range you can work with. Now you know a seller is going to want around $75,000 for a machine in the kind of condition you expect for its age and decent condition. If they have a great undercarriage or maybe a recent engine or drive train repair they will want more. The dealer asking $102,000 knows that only fools pay list. You know the dealer didn't pay any more than $70,000 because they have a markup of thirty percent. Now you know where you can negotiate. If you paid $102,000 for the iron you took a big risk by paying over market and you better hope whoever looked at the machine knew what they were doing. On the other hand if you see one of those machines being offered for $65,000 it might be a good deal but more than likely it has something major about to take a dump.
I think I'm going to write another book on this stuff next winter.