What I would do is this: write into the contracts that as condition of the sale $X must be paid into a fund every year for say 15 years. X would be what would be required to pay all that you listed PLUS what would make the fund self-sustaining in 10 years.
Then, not only do you have ALL the fundings taken care of you might even be able to make the fund into a sort of insurance-as-well thing for emergencies. {Of course this requires both foresight and patience.}
I was thinking about an initial deposit being a portion of the contract, as an answer to his/her question, but I don’t know how well that would work in any event, nor do I think it would be any better for the homeowner. But it would, at least in theory and temporarily (until the funds run out), solve the posed problem I was asked.