Advertising to get funding for the app instead of charging.
Acorn is an app is is essentially free to use to invest, store, and budget your money for free.
YouTube is a site that shows us user created videos for free. Both of those companies made deals with other companies and artists by accepting their funding instead of accepting funding from their users. Yousician has the potential to acquire new music, new teachers, and advertisers by allowing artists, record labels, and manufacturers to push their product during, before and after each lesson. The revenue from those interactions should at least bring down the cost of learning on this app