There used to be "just a book" option before at $49 if I remember correctly, that's when I bought it. So I'm pretty sure Nathan's decision to remove that option is intentional, or an experiment of sorts.

The book is really good; however, I would not have bought it then if I had had to pay $180. Is it worth it? Yes, if you're 100% absolutely certain that you want to create a business around a book.