I think sponsorships are your best bet. The only problem is that with 80 ppl per month, you still have a pretty limited audience that might draw sponsorships. I would not recommend charging for regular events as that will likely depress attendance. Offering separate speaking/seminar opportunitie...
This is my wheelhouse but unfortunately I am heads down putting the final touches on my MastermindTalks event. If this hasn't been answered in the next 2 or 3 weeks, I will come back in to reply... Good luck!