It isn't expensive to run on Cloud Functions at all. You do it right and it scales pretty insanely high with very little additional cost. I've built multiple successful businesses with AppEngine and CF, so I'm keenly aware of their implementation details.
My point is that this is the solution to use and there really isn't any reason to switch. But, if you really were that bothered that you wanted to to switch, you aren't super tied to it in your codebase. I'm not saying the cost to switch is zero, I'm saying it isn't impossible.
My point is that this is the solution to use and there really isn't any reason to switch. But, if you really were that bothered that you wanted to to switch, you aren't super tied to it in your codebase. I'm not saying the cost to switch is zero, I'm saying it isn't impossible.