Yeah Dave, I understand you probly didn't come into this sitch with a business plan, or fundraising plan.., and it's plenty to do without thinking about it too much.
My question was meant to be simple, but it would require some basic bookkeeping, and maybe some site usage monitoring, at least enough to get a sense of who the heavy/regular users are, so they can be free to donate at will as they do now, but with an available target for them to look at over the year, (which you could project yearly as you foresee new cams etc.).
Paying upfront is exactly as you see it, people complaining. Setting out a list of regular users (if possible automatically by software), and priming them with a target, prevents them getting the sense of being billed. They wouldn't need to be reminded directly, but they could be if that is what helps people to keep up.
So, just a simple box on the main page maybe, with several targets, ie: for the regulars, for the casual/drop ins. "Our fundraising targets for 2014" with a colored bargraph showing progress... You could even suggest different layers of donation, so people feel a pinch if they aren't giving enough...
Like, Suggested Donation
Heavy User, -site visits more than "x" per month
Regular User- site visits more than "x" per month
Casual User - site visits more than "x" per month
Seasonal User - site visits more than "x" per month during season
etc....
Since you have access to the data on usage, and perhaps understand it better than us windjunkies, the categories could best be projected from that point of view.
Just suggesting, of course, none of this is a lock...but I do remember I had to push you a little bit just to put the "donate" button up in the first place....just sayin
Roger