We put one in for my step daughter three years ago. It was a used 1500 sq foot nice one. It was $32,000 delivered and setup. We had to put in the pad, electric, plumbing etc. When I graded for the pad, I built up the low end about 4 ft to get it close to level. They said ideally the pad should be level within 18", but I've seen them on much worse places then that. There's one up the road from me sitting on the edge of a large hill. I'm gussing there's six or seven foot height difference from front to back. But then it's also on a full basement with proper footings. I'd really check into how to construct with piers if the hill is too large. Your dealer/manufacturer should be able to provide the recommendations you need.
Good luck
Bryan