A suggestion...
On the left side at Ebay you can select "Completed Listings" which includes sales and aged/timed-out. Then you can scan the right side listings to see which are actually "sales".
From my looking for a few years, I've developed a bit of a formula that seems to work for the newer equipment. I figured 200,000 miles uses up a car, or a tractor engine - that would be 3333 hours at 60 mph - so a 333 hour machine would be 90% left, 10% off of then new price. And then for attachments I figure at 1/2 of current price. May need tweaking, but seems to work so far.
Others?