It's really hard to put a value on Antique Big Trucks. Not as big, of an market out there, as pickups, panels, Suburbans, etc. Take up more space, can't park them in a normal garage, not as practical, as a small truck, for running errands, etc. Would not be worth as much, as a small truck, in the same condition. I've probably bought, & sold at least 20-25 Antique Big Trucks, in the last 10-15 years, & believe you me, I can never guess what they might bring. It all depends on who's looking for one at the time.
