Also you should charge more for this book, I think it’s worth at least $30. The extra value added package could be $50 and include the templates and case studies or a personal resume review. See Rock and Roll with Ember.js: https://www.balinterdi.com/rock-and-roll-with-emberjs/
For the contrast: you have a good point. I'm seeing if I can do something, but I am seeing a good variety of sales across packages. I might just leave it for today, come back to it later.
For pricing: I'm aiming to optimize for reach over revenue for this one. I'd like to keep the book affordable, and give people a good deal. But by people paying, I'm hoping to target those who will actually read it, over just download numbers. I especially would not want to overcharge as resume advice is... a subjective field, and no one can guarantee results (maybe some gurus say they can, but I don't want to be that guru).
Originally, the whole book was supposed to be two pages in the next book I'm (still) writing on growing as a software engineer, in the job search section . I just hope the other parts won't expand as much as this one has :)