I don't have a ton of experience in this space, but I did go down the road of almost launching an app. The budget you need to launch a successful app right now is enormous. Exact numbers that you need to budget would depend on what exactly you are trying to do. The cheapest way to get an app launched right now is to do a web based application, especially if the app does not need specific hardware to run. Having a web based app eliminates the need to build an app specifically for IOS and Android. The cost all depends on how many hours the developers have to put in for the app, how many pages, and how difficult the project will be. You also have to figure in costs to retain a developer to fix bugs and push updates to the app.