You could board horses and if that does well build some more stalls.
-Rent your stalls outto boarders, you will of course have to provide feed and straw for their horses, but you can charge 200-400 for that
-give riding lessons, if you know how. If you are a qualified instructor, you can buy a couple of lesson horses and give lessons. You can charge 20-40 per hour or half hour lesson. If you are not an instructor, you can hire one.
-Buy/Sell horses: if you know anything about horses, you can make money buying, breeding, ect. Make sure you know what you’re getting yourself into if you want to do this.