Where exactly do you live? I don't really need a zip, but like a town or something. I live just about an hour away from NYC in Sussex County, NJ and the barn I board at, though it isn't the nicest looking and all, they do have an indoor and numerous outdoor arenas. The most expensive board there is $440 and I believe the lowest is under $300 (but that's pasture turn out with no stall). There are also a lot of kids there that are under 18. I'm going to say mostly around 15 or 16. The people are nice, as long as you comply with their rules, and I could tell you more about that.
I'll definitely help you find a place.