The book is available Leanpub.com, where you choose how much you’ll pay and see exactly how much the author receives. They offer the book in PDF, MOBI, and EPUB formats for a single price, and you can always return to download updated editions, when available. The edition currently available on Leanpub is the 2nd Edition, which is in progress. That means the Leanpub book will be incomplete, and you’ll receive a new build every other month or so. Go to Leanpub→
You can also purchase the book from Amazon in print or Kindle formats. Go to Amazon→
Audiobook version is currently in pre-distribution.