I worked as a groom at horse shows for three years, and personally now that I look back was a waste of time other than the experience. The pay was terrible next to the amount of work, working from 5 or 6 in the morining to 11 at night wears on you. Grooming six to 10 horses three to four times, cleaning all their tack after each class, braiding rebraiding, you get the point.
The only way I know you might be able to make any money is become a good instructor and not own your own lessons horses. I consider horses a hobby and it makes everything easier. But I am interested in what other people say!