I'm glad the difference of opinion (and in what constitutes a folk-club) has been resolved.

Like Jed, I perform in a lot of folk club/coffee-houses such as Godfrey Daniels in Bethlehem, PA, Caffé Lena in Saratoga Springs, NY, and Club Passim in Cambridge, MA.
I incur travel, lodging and meal expenses.

The building are owned or rented by the club; they all have very fine PA and lighting systems, usually with a soundman. These all cost money.

As do advertising, print or electronic.
They sell coffee, tea, juices and cookies/brownies, etc. Minimal if any profit on these.

I work for a guarantee versus a percentage of the door.
Usually the percentage is greater than the guarantee, so it's profitable for me.
The balance of the percentage goes to the club to help defray its expenses.

On more than one occasion, due to weather usually, there has been a tiny turnout for the show, and so I didn't make the percentage.
I also refused to accept the guarantee, and just asked for gas and food expenses.
And I did the same show for the four people who showed up that I would have done for a full house. (I'm a performer for God's sake, and they're an AUDIENCE!!)

I believe in becoming a member of each folk club I work in, so I pay my annual membership fee, generally in the $10- $20 range.

The club uses membership fees to pay their performers, and all the other concomitant expenses.

So if a folk club charges admission fees, it's because they have to to stay in business.
At least here in the U.S.

Seamus