Stating the obvious here, but providing mail-in payment information would increase the membership by at least a few.
Not meaning to rush anybody, just speaking from personal experience.
edit -- If I was doing it, I would make either a Membership sub-forum or just a sticky post, locked so no replies can be posted to clutter it up, listing the pertinent information about how to join, and nothing else: cost, payment options w/relevant details for each option, and procedure (you will receive an e-mail within 48 hours...). Then I would put a separate post or a reply to the first post describing what one gets for their membership or whatever else, but I think it is best to make it straightforward and easy for people to send money to the club. So many organizations overlook this simple fact.
Or, you could do something completely different. Either way...