So far most of games or minecraft servers i have checked out with a form of paid monthly "subcription" have a mechanic that allows players to sell a subscription token on market, this way, people who are willing or able to donate can buy Donator Token and sell it on /ah for in-game currency, this allows players who arent willing or able to spend money on donations to get the donator rank by indirectly contributing, by encouraging more frequent donations, because players who have in their ability to donate can gain additional benefits for donating more. (this can be seen as more "pay to win" but thats incorrect, since now players who dont wanna pay can gain donator rank without paying, so its even less "pay to win")
Also if anyone out there thinks this can cause inflation because now in-game currency is "purchasable", just no, money was already in the economy if someone was able to spend it on /ah, so dont even try to comment on it Mr. Keyboard Warrior.