Pretty much all technical books are expensive. The authors put in a lot of time, effort and expertise to write the books and there is also a limited audience for the books. For any profits, author and publisher, these type of books tend to be expensive. The cost of the book is not in the printing so much and to provide electronically additional work has to be done and so people who purchase have to pay.
BTW - I consider this book to be worth every penny.
I have not failed. I've just found 10,000 ways that won't work" --Thomas Edison