We are actually taking it beyond NextJS. Once your logic is implemented in UNA we can build UI as a universal app which with React/NextJS+ReactNative, styled with TailwindCSS. So, you'd have the react web UI as well as native iOS and Android apps. The app would use UNA API from your site for data.
The cost can very significantly depending on how much functionality you want to be available within the app. Expect it to be within $40K-$200K range. This is very cost-effective approach, considering that simple social apps development cost begins from about $40K per app - so for iOS/Android/Web you'd be looking at $120K+ price tag normally, which is still likely to be way more simple than what we can build on top of UNA. Also, the benefit is that you still have all the UNA features for your standard web UI, administration tools, builders, etc.