I think if you could provide an option to "premium subscribe" to nostrgram many would opt in even if that didn't provide any extra perks. In fact I think that "premium" should not have any extras as providing all the features to everyone could help more people realize how cool nostrgram is and push them to give back. You could give the supporters a badge or add a tab listing the supporters if you wanted to though. So what I would do (no PR expert here) is add a button in the dashboard (maybe next to notifications icon) that when clicked would offer different subscription options, similar to what your zap pop up looks like now. And automate the process of charging that amount monthly/weekly/daily. Not sure how that would work, but #[2] supports budgets and signs zaps for users in the background, so I'm sure there's a way. Of course if such "soft" approach doesn't work you could try something else.