mobile and web app

Dear Sir or Madam,

We are a small online school.
We need an app that can be used in both smartphones and desktop computers.
That is, the application is like skype but we need a lesson constructor for our teachers
The lesson builder that we like’s www.learndash.com lessons builder.
We need this app for teaching our students.

So we want to upload video, exercises, audios to this app, have a lesson builder in it.
Ideally it should be like skype but with a lesson builder in it
We imagine this app like a platform for teaching with some pages leading us to video chat, and the other page leading us to a log in with the lesson builder and stored lesson material so before going to an online lesson with our students we can build a lesson and then have it open and calling to our students with the teaching material ready to go
Could you create such app for us?
If yes how much ‘ll it cost.

Thank you in advance,
Sincerely,
Sevil