Pay per use – restrict amount of function calls by membership level

I like to restrict my WordPress site by paid subscriptions.?
Based on the subscription level, members can certain pages with specific functionality. So far so good, this can be easily done with different plugins.?
But on the restricted pages, members can execute functionality which is basically returning customized content based on their individual input. The functions are implemented via forms and PHP functions.?
Is there a way to implement some kind of counter which limits the amount of function calls by subscription level? e.g. basic members can only call the function 50 times per month?