"In-app purchases".

Google/ every-company/ heck, even EU- fail. I'd like the prices of every possible addition (to any software) to be clearly stated upfront.

I have several music apps: I do understand a new-instrument/ effect release can't always be accounted for initially, but I'm very sure it can be added to a list on the playstore front page.

If you go to the details page, scroll down to where it says "In-app purchases", you will see stated "$20.00 per item".