depends on area but surely fully serviced livery would make money?
TBH, probably not around here. You'd need to do equestrian events I think - horse-and-owner (residential and non-residential) courses, holidays, 1-day events, that sort of thing. The locals will come and hire the arena now and again, quite a few would probably come for some instruction if you had a good instructor for rusty adults who just want to enjoy their ponies more, and for working / driving / training instruction, but you won't live on the income stream from local horsey folk alone, I don't think.