
Can you make a one-time-donation option for now, and perhaps sometime again in the future as well as having the 'subscribe for a year' option?
You could have the donations cap at some number that you deem reasonable to sustain the site for some length of time (maybe 6 months to a year? idk) and then start another donation pool sometime in the future when the current pool runs dry.
I think you might have a better turnout from one-time donations vs auto-withdrawing subs. I'm not saying get rid of your subscriber thing, just do the donation pool as well
Maybe also give small rewards for people who drop a certain amount of money in the one-time donation?