estimation – best cloud database solution for mobile development

Looking at firebase and its “pay-as-you-grow” model and wondering if is the right backend solution for a solo mobile developer.
Is it right for someone that is developing an app alone? Do you have an idea about the cost of a simple plan for a chat app? Is there any data ownership “problem” with this king of solution (AWS, Azure, Firebase, etc.)? Can you easily switch to another solution afterwards?

Hope the question is clear, thanks a lot for your insights!