$1/mile is indeed cheap for a trainer to ship to a show.
Shipping is expensive, as others have mentioned. A trainer I know is considering getting rid of her truck and trailer because she loses money on it.
I paid $350 two weeks ago for my mare to go under 16 miles round trip to the vet. At least one direction, she was not alone on the trailer. I didn’t expect a discount because she wasn’t. I accept that the rates are what they are because the person is doing me a service, putting wear and tear in his rig, is accepting liability to ship my animal, etc… but most of all because it is a BUSINESS and he has to make a living.