I work for a giant airline and used to work directly with the maintenance cost data. I only know about the 737 size, but if you want the plane to be able to fly, the plane has to go under a major overhaul every 2 years (plus a slew of other stuff). The cost of those are frequently in the 6-7 figures each depending on the year. If you don't need it to fly, I know there are restaurants made out of 737 shells that operate just fine so the cost should be feasible for a small business level of income.