I tear down semi trailers. On a 40 foot trailer I average 5000 lbs steel and 1000 lbs aluminum. I separate all the metals by hand and prepare it to the size my yard wants. There are many factors to consider, like the flooring and the construction of the trailer (aluminum bows vrs. steel for example), as well as the size (height and length). If you drove it in they probably docked you 100 lbs per tire and 2000 lbs for the wood floor. Of course an alminum floor and aluminum floor joists would be a different story. I average about $1600-$1800 per trailer with wood floor and steel floor joists. I spend roughly 40 hrs per trailer and about $50 on blades wheels etc. I hope this clears things up. I get $300 per ton for prep heavy steel (3' x 5') and $0.65 for 4'x4' alum.