What I'm recalling is what Jesse mentioned, though I didn't remember Bowen sending the horses to Gallon Jug for rehabilitation.
I imagine there would be some demand for a small equestrian center on North Ambergris, riding on the beaches and all, as long as the owner had the land and the facilities to house the horses and the money to provide good care and bring in adequate feed. But I wouldn't think it would be a big money maker, any more than horseback riding is a big money maker anywhere.
Lots of costs and not much revenue. Probably better to rent golf carts at US$65 a day.