Nice self-care facilities are hard to find in my area, so there is typically a decent demand for them. I would definitely look around for comparable options nearby, to help set your pricing.
Before you jump right in, don't forget to factor in overhead costs!
You will still be responsible for regular maintenance of the property (ie. trash service, fence repair, roof leaks, replacement gravel for frequently traveled driveways, squeaky hinges, broken lightbulbs, yard work, a replacement water spigot when someone backs into the original,) plus all the tools & manpower needed to address these things. Will you implement vaccination & deworming requirements to keep your facility healthy or is that at the boarder's discretion? How will you handle large quantities of manure? Will there be barn rules such as visiting hours, a stallion policy, stipulations on what/where boarders can store, notice that brooms available so they clean up after themselves? Where do they keep feed & tack, and is it separate from other people's feed or might "borrowing" become an issue? Can they store their horse trailers, RV's, and rusty old boat on this property? How many horses are allowed on each pasture?
You will also want a thorough Liability insurance policy, attorney-drafted waivers, and contracts for boarders to sign, to protect your assets! Keep in mind, if one boarder isn't feeding their horse and Animal Control is called, you may be held responsible for that animal since it's living on your property. If the boarder's neighbor kid gets dumped off someone's horse and hits his head on a fence post, you could be sued.