One possible suggestion is a one-time payment option. In a couple of my projects I have daily/weekly/monthly plans that allow people to pay up, use the features

One possible suggestion is a one-time payment option. In a couple of my projects I have daily/weekly/monthly plans that allow people to pay up, use the features and then go away without worrying about long-term financial consequences. Maybe an option were someone can pay up, export their data and then whenever they want to import it back in they sign up for another short plan.