Aside from functionality, the design is one of the main things you have to think about when creating an app. With the bad design, months and months of your work can be ruined, since that is the first thing consumers notice upon installation. Therefore, you need to consider a broad spectrum of things like: User research Competitive audit User experience Mobile app interface design Once you take all of that into consideration, you will be able to calculate the amount of money you need in order to design an app.