For that distance I would look at a trucking transport company rather than someone with just a trailer. When I have moved horses long distance I always used racehorse transport companies as they were always going through and often have room to chuck on another.
I'd google horse transport and see what you have in your area.
My last horse though was in an area that was off the beaten track, too far from the main route for the trucks. By the time I paid someone for their time (there and back obviously) and their vehicle/float useage, and petrol on top it was cheaper for me to just hire a car and a float and move her myself.