It’s a “ how long is a piece of string“ question. It depends on so many things. The famous ones are going to be multiples of the guys who no one has heard of. It also depends how far they are from you so where you live matters as well. We paid 150 for Richard Maxwell to come out a million years ago but I’m sure his prices will be much higher now (he was worth every penny and the lessons about loading he taught me that day has meant I’ve never had a problem loader since … the only way to know for sure is to find a trainer and ask them.
Agree with blitz, local guys around here charge around £75, for my loading issues they were a waste of time and money, i paid Richard maxwell £400 (I'm a long way from him) and i would pay double that as he's so good. I got him out recently for another horsebox issue on a different horse as i knew he would solve the problem