I've said so before and I'll keep on saying: G/A will never bring in enough fees to operate an aerodrome commercially, with only professional staff. Not in a month of Mondays!
Either part of the cost is borne by local authorities, as is the case for a good many fields in France ("aérodrome municipal" they call it, and it might be comparable to what they do in the US), or you have the major part of work done by volunteers / club members - and that is how many fields work here in BE.