It's high, but not terribly high, imo. When it comes to professional development, this could be considered quite cheap. A freelancer who charges $100/hr can pay for this in 30 minutes, and if it gives more than 30 minutes of productivity in the future, then it was worth it. (Figure out your rates, and do the math. Odds are that it'll be worth it.) Furthermore, a lot (if not most) companies will be willing to purchase such a book for their employees, because the math is even better for them.

If you're a tech writer like Sandi, you can absolutely get away with $49/copy, or even $99 or $199 per copy. They usually offer extended examples online or what-have-you to justify the $199 price, but it happens all the time.

For professional development books like this, you can't really think of it in the same terms as leisure books, like fiction, where the only benefit is having a good time. There's a benefit that goes beyond entertainment -- benefits that are monetize-able by the reader. If I read this book, and I learn something that allows me to do something in 30 minutes that previously took me an hour, then I've effectively doubled productivity. That means I'm more valuable -- and therefore, the book is more valuable. More valuable = more expensive.

Hope that helps explain why it's the price it is. That said, I'm passing too. I tend to prefer physical books for professional development, or ideally, a physical + digital combo.