Finding Events which are Free to Nobody

There's nothing on the forum with "Membership Fees: ", the heading from the Admin...which controls which subscribers can attend an event without paying (part of the Membership/Events integratation).

I need to create a query that will identify any Events which are free to nobody. The nature of the business is that every event should be free to the members who have that type of membership or a multi-type membership. Anyway, any event free to nobody is an error in the client's business model.

Can anyone provide SQL to identify such events? Or substantial pointers?

I'd like to suggest that this functionality might make a nice add-on/option on the Extras or Advanced tabs.