Mobile app design costs vary quite dramatically depending on how large the app is and also what functionality is to be included. However, as a UK Digital Marketing Agency that has been designing apps for quite some time, we can give you some guideline pricing;

1. To design the initial concepts which will provide direction for the rest of the app, you are looking at around  15-25 hours purely from a UI point of view. If you require these concepts to be wire-framed prior to, likely double. Generally we produce 2-3 concepts initially for you to review and this includes 3 iterations but more of course can be requested. 
   
   
2. Once a concept has been approved and design direction is established, we then need to move on to each page/screen of the app. This is generally much quicker on average taking around 5-10 hours per screen, again with 3 iterations per page/screen within the app.

Mobile APP UI refers solely to the actual user-interface of the app being designed. Prior to UI Design, generally speaking (Unless trying to cut costs), we go through UX (User-experience) and wire-framing design. This establishes layout, customer journeys and flow. Once this is established, the UI Designers then convert those Wireframes into actual UI Designs ready for you to preview – this is the final product of your app in design format, usually produced in Figma or Adobe XD. They are all prototyped so you can envision you app before we touch a line of code. Check out our UX UI Design services here.