Who pays for any other mx outside the annual (oil changes, 100hr (if you decide to do them), incidentals)? How about the aircraft insurance? If you're just paying the lease and fuel (no insurance, no maintenance), that's a pretty good deal, about $60/hr depending on what fuel runs in your neck of the woods. 600 hours is a lot of time for a 172 in a year, so expect some stuff to break.