Yep I've never heard of a trainer paying
to show someone else's horse, or even doing it for free. At the very least the owner would pay all of the fees that go to the show secretary (class fees, award fees, stabling fees, etc.) It can easily add up to >$200 for a local show. On top of that, most trainers will want to be paid themselves to show your horse which can vary wildly depending on the trainer.