Go through the books. Do you need doormen? (no) are the coop owners willing to do away with them? (maybe, maybe not)
Look at what the money is going towards. Some things can not be done without. Insurance, lighting the hallways, other things also. Some things can be removed as they are unneeded luxuries. Then at a meeting see if they are willing to cut back and make it more affordable. It is also possible that it is an old building needing a lot of things fixed and it will cost far to much money no matter what. If the roof needs repairs, the furnace needs replacing, the elevator is shot, the plumbing needs to be completely replaced and the wiring has to be completely replaced there may be no way to cut back on expensive maintenance costs.
Maybe they are spending less than they take in so in the future no special assessments will be needed. If so it hurts some now but a lot less later.