Given the quality of the product I don't think charging for this
publication is unreasonable.  I've paid, but it occurs to me that it's
been a long time with no prompt to renew (expecting people to remember
spontaneously to send in a contribution on an annual basis is
unreasonable!)

With regard to credit cards, why not use PayPal?  That way you don't
need a merchant account and the associated fees/problems.

If the long term survival of this resource is in jeopardy as a
result of the burdens on the maintainers I would strongly encourage
consideration of lower maintenance options.  While these have drawbacks
they are very low cost for all involved and have proved to be
self-sustaining over many years, for example:

1.  Create a real Usenet newsgroup.  This list alone can probably
muster the approximately 120-150 yes votes it would need to create
a newsgroup in the "Big 7" hierarchy (rec.music.makers.mechanical
or some such).  If unmoderated this is zero maintenance, propagated
worldwide, archived at many sites, and free.  Downsides are the lack
of editorial curation and putting up with the bozos that spam and troll
such groups.  Alternatives are a moderated newsgroup (more work) or
a newsgroup under the alt domain (poorer distribution).

2.  Use an automated listserver.  I subscribe to several now, run through
Yahoo groups which seems to work quite smoothly.  You have to look at
an ad, but there are web interfaces, mail digests, and message-by-message
distribution options.  The information is archived, though not indexed
or curated.  Requires some work from list owner(s) to answer the same
questions over and over again related to subscriptions, can be public
or by membership only (effective at eliminating most spam), can also be
moderated, but this is more work for someone.

I'm very happy with MMD and happy to pay for the added services provided
by our editors, but would be very sad to see the community and resource
disappear because it was too much work/low reward to maintain.  There
are other alternatives that handle a lot of the administrative overhead.

Cheers!
Roger Wiegand