Don't be shy about asking. Most of us aren't impecunious kiddies any more. I've ended up "covering the difference" on a site I visit/admin and people are usually willing to help if they think about it.
It's probably sensible to setup a crowdfunding donation thing which supports either recurring or occasional payments, and can keep track of totals and stuff.
Though that would also be adding another thing which could go wrong, and I presently have enough already gone wrong things I need to focus on resolving for the time being.