If it is in good enough condition to haul on the road without falling apart, check with your local mobile home dealers for who they use to haul mobile homes - they usually have slip-under axles and tires (on wheels) that will fit most trailers if yours are dead or gone. Cost probably about $800-2000 (because of width and length), depending on dump fees at your landfill an road haul permit fees.
In some areas with really strict landfill regulations prohibiting large objects, you may have to have a demolition firm come out and demolish it and cut the frame up on site and haul it off in pieces in a demolition disposal truck, which would usually cost $1-2,500 - assuming no asbestos - you might have to get a certification from the manufacturer that your year and model was built asbestos free.
Mkae sure the contract specifies it is to be disposed of at a legal landfill or recycling center. If I were you, I would trail them to the landfill to make sure it actually gets disposed of there and not over some bluff - you do not want some government employee knocking on your door because your trailer was illegally disposed of, and laying a $10,000 fine on you PLUS requiring you get it all cleaned up - to the last scrap, from the bottom of some ravine or bluff. THere was one in our area a few years ago (though the guy dumped it over a river bank himself to get rid of it) - totalcleanup bill and fines exceeded $100,000.