Gainsborough Folk Club meets at a social club which requires that some of the Folk Club regulars are members. What we decided to do was introduce a yearly membership charge out of which we would pay the social club membership for that person who then gets free admission and a reduced rate on guest nights. Non members pay each week and are logged in on a list so that the Social Club knows who their guests are.
Seems to work. We never had a regular charge and this is easier to operate as less money is involved for each meeting.