Idea: add cost estimates before you hit 'generate audio'

[larryhudson]

I've actually already got the code for this almost ready to go - it's inside the wikipedia utility functions - src/utils/wikipedia.js

I just need to move it into a separate utility function file, and then use it on the article page next to the generate audio button. Should be easy.

[larryhudson]

This is done now.