No, however while one can debate the pricing models of books in general, AFAIK the cost of an ebook is about equivalent to a regular book (they both have layout costs, and actually printing and even distributing books, is so ridiculously cheap that it's absurd -- you'd think there's a bid difference -- but there isn't). So a better question might be, is $50 for a high-quality, highly-technical, low-volume, narrow-audience book normal -- and I'm afraid (for book buyers, not publishers/authors) the answer to that is: yes, quite.