Ceiling insulation in old 5 unit in Colorado

My boss has an old unit and it has plaster ceilings and a flat roof. No real way to access the drop ceiling without cutting it.

He said foam would be good but expensive.
I suggested Owens Corning pink blown insulation with a 3 inch hose and drill a hole for pressure. He thinks we would have a lot of holes and patching.

I was thinking trying to cut one hole to let a guy stand on a ladder and blow the insulation then patch the ceiling.

The apartment units are small. Any other ideas? Thanks.