If you have a place to do the blasting you can same $ by doing it yourself. Cost me about $75 to rent a 130 CFM compressor for the day. Borrowed a pressure pot from a friend and bought about 8 bags of sand. You will need a quart of primer and about t2-3 quarts of color. Picked mine up at Tractor Supply. Use the hardener.

Another option is to drag the trailer to a local blasting yard and they may do it for about $150.00. You could always strip it yourself with a wire wheel on a grinder but you would not be able to get all the rust off. In that case you could use Zero Rust paint as a base and after it fully cures cover it with a top coat.