OK, that's a bit more to work with. My gut feeling is that it's a fairly big number for the scope of work. That said, there are some wild cards. You may be in an area with extremely high disposal costs, or there may be an unusual volume of material to haul. OTOH, if the buildings are accessible (not buried in trees and brush) and the lot is flat, there are only a few hours of machine time needed to demo. and load everything.
A few thoughts. First, can you do a controlled burn? In these parts the volunteer fire companies will burn old houses down as a training exercise. If you are allowed to burn it yourself, with a fire crew on site, or can get the dept. to do it, the job becomes a lot cheaper. Second, make sure that you have at least two bids from reputable contractors. Make sure that you are dealing with outfits that are fully insured. As you can imagine, there are no limits to the stupidity some of these guys can dream up, from wrecking the wrong house to getting somebody killed, it's all been done before, repeatedly. Finally, if you are limiting your contractor search to strictly demolition specialty contractors, remember that many excavation contractors do the same work. I us two subcontractors locally that each end up demoing a house or two a year. Typically it's homes that burned. Excavation contractors often have a hydraulic excavator that equipped with a "thumb" that allow them to grab loads. Good luck, it sounds like an interesting project.
