If I understand right your hall with about 75 publishers sends in about 1,300 to the society and uses an additional 500 or so for local expenses each month, for a total donation from the congregation of about 1,800 a month.
So 1,800 / 75 = 24. Of course every publisher doesn't contribute, I never did as a teen unless my parents gave me some money to put in the box. So that means some publishers are giving more.
24 or something a bit more a month doesn't seem like much to contribute even for a dub. I could see this makes sense on an average basis.