Why not auction/sell club memberships on eBay? it would:
(1) advertise the Club, even if no one bought/won memberships. Would cost the Club just 30¢ (up to $9.99 starting bid for the auction) or 55¢ (up to $24.99) per auction listed.
(2) increase the membership.

A one-year membership is $20. You could start the auction at $9.99 (or more). You could have a buy-it-now at $15.00 or so. Call it an introductory special offer. Some minor qualms and details would have to be worked out I am sure, like stating in the auction description that it is eligible only for new members, that it is subject to ethics review, etc. Dutch Auction? Have it on a regular basis.

Comments? (I already posted it on the Club bulletin board.)

Robert