Follow https://twitter.com/sinequanonh He sometimes posts revenue numbers of his https://hyperping.io/ service.

With the low price point you'd attract users who bail at any price increase. It leaves little money for customer acquisition and support cost. Spending 10 minutes on a customer email ("do you plan to add feature X?") or dealing with failed credit card transaction (month 6 fine, month 7 "insuffient funds" error) already wipes any earnings the customer might have brought.

I'd try doing only yearly payment like https://servercheck.in/pricing