Pay What Feels Right
If you are open for an experiment in abundance, you can choose to download the book for free. You will receive an email a month after the download inviting you to consider giving the author whatever value you've gotten from the book (what you give will go integrally to the author).
If you haven't read the book, or it didn't match your expectations, you can choose to give nothing. If you like the book, feel free to gift whatever amount you feel is right for you.