I just looked at some old spreadsheets, I don't have any for commercial buildings anymore, but the largest apartment building I still have in my records (200+ units) insurance was $27,000 a YEAR. A commercial building the size of an assembly hall is going to be less. Utilities on this same building (which includes tenant water) ran $90,000 a year which includes 46K for garbage.
For an assembly hall, insurance, utilities and supplies might run a grand or two for the weekend.