if every local user would donate 1 cent each month we would get more in donations than our total costs are

This is a really solid selling point. Every admin should do this math and ask for donations like this. I know I often fall into the trap of feeling like I need to donate more. Because it's a bigger bite of my budget, I end up procrastinating and not donating. But reading this, I would more readily donate an amount that's more comfortable to me but also accounts for other users' portions