What this is built for
One specific thing with a number on it. A furnace, a roof, a set of gear, a van repair. "The furnace, $4,500" asks better than "support the post," because the member reading it knows exactly what their hundred dollars buys.
Groups that already have a roster. Veterans posts, volunteer fire departments and their auxiliaries, Rotary and Lions clubs, booster clubs, youth clubs, neighborhood associations, alumni groups. The membership list is the whole requirement, and every one of these already has one.
Something that broke, or a date you can't move. A furnace in October, a hall that fails inspection, an entry fee with a cutoff. These are the things the annual calendar wasn't built to absorb.
Contributions start at $100. That's the scale this is built for — a member putting in a hundred toward a furnace, a local business covering a tenth of it. Forty-five people and the hall is warm.