It could be a heck of a lot. Or it might be quite cheap GIVEN THE SIZE AND COMPLEXITY of the app.
If I were I customer I would ask for a specific quote based on the app that I had. I would ask for each step to be broken down into stages and the length of time needed to do each stage. I would ask for deliverables at each stage. I would try to figure out what I was paying the provider. If I saw any inclination to hide this info I would move to another provider. Like anything else I would be trying to establish if I were getting VALUE for what I was paying for.
If I were I customer I would ask for a specific quote based on the app that I had. I would ask for each step to be broken down into stages and the length of time needed to do each stage. I would ask for deliverables at each stage. I would try to figure out what I was paying the provider. If I saw any inclination to hide this info I would move to another provider. Like anything else I would be trying to establish if I were getting VALUE for what I was paying for.