I suggest that you look in the rural areas of Upper Roxborough, especially by the Nature Center. You might be able to find an old unimproved farmhouse. Also, Fairmount Park has an impressive inventory of Park Houses which they rent to try to keep them up, which they do a poor job of. If proximity to horses is most important, there are at least three stables in Roxborough for people who ride in the Wissahickon; obviously they are proximate to the park. Green Lane next to the Park (in Lower Roxborough) has both stables and cheap apartments, but they are from the 60's. River Road isn't particularly horse friendly (more boat friendly, but it is only about a mile from Courtesy Stables, if you are willing to hoof it over a semi-abandoned and very rural Port Royal Ave), but it is rural, picturesque, and cheap, sort of like the rural south (Alabama?) in Philadelphia. Very jarring. Old Florida also comes to mind.