Just out of curiosity, how does a club that operates that way
allow for expansion? For example, if they get a dozen or so
new members, they're going to want another glider, but
they won't have any money to buy it.

They will have additional monthly revenue which can be used to finance
equipment. Yes, it will be more complicated than just having cash, but
many potential members would never join if they had to pay a
significant sum of money before they even start.

Bartek