I’m developing a iPhone application that will use a Google App Engine backend and planning to sell my application for $1 on the App Store.
I feel there is a risk that my Google App Engine cost exceeds my revenue from the application and therefore it is not possible to keep the app backend going in long term.
The question is – For how long am I obligated to run the backend? It is not possible to run the backend forever, so how long do I have to have it available?
You have options other than just an upfront licence cost. Consider using subscriptions so that you’d continue to receive an income for as long as people actually want to use the service.