Add funtions to an app progressively

I need to add functions to a mobile application📱 that I have hosted in Google's IDE "Project IDX" using Dart language

It is a basic file explorer 📂 to which I want to add some buttons such as recording🎙, reproduction ▶️, search🔍, and some options in the lateral menu

I would like to adjust at a price according to my budget, for example several packs of work at 10 dollars each

Greetings and have a good day! ♥️