346 hours is both an underestimation and an overestimation. I can say that I definitely did not sit down at the keyboard for 346 hours to put this together. But how do you account for time spent thinking about the content, planning, visualizing, etc? What about the fact that most of that time was 'overtime'? ie. over and above my full-time job.
The other perspective here is that this took a lifetime of work. I've been learning about the source material for the past several years. Obviously it wasn't just to write this book, it has many practical applications besides. I've 'practiced' teaching people and writing for years before this, all of that certainly contributed. This quote sums it up nicely: http://www.marketingquoteoftheday.com/pablo-picasso-on-prici....
I don't think it's fair to try to trim down a project like this to an hourly rate because it simply doesn't work like that. I could stop putting time and effort into the project right now and I would still see some money come in, arbitrarily increasing that hourly rate.
Just to drive home this point having a book with my name on it opens up new opportunities. If I were to write another book and spend the exact same amount of time putting it together my 'hourly rate' would probably increase because I now have more people listening to what I have to say and trusting that I will provide something of value. So investing time now into this project is a long-term investment that I may not make back on the sales of this book, if you know what I mean.
I've no idea if it's feasible to write like this for a living. There are lots of people (even in the tech education space) who make a living selling their own products, but typically not just books. Look at people like Marc-Andre Cournoyer or Peter Cooper who have written books but make their living through some combination of teaching mediums (video, webinar, books, training, etc). For many of them their first product was an ebook.
Just to clean things up, this book was written out of love. I felt like I couldn't not write this book once the inspiration came. That being said, there was also a financial motive. I wanted to be compensated for my work, but also wanted other people to place value on the material. Too often free material is considered worthless because there was no exchange made for it. "If you don't give anything you don't get anything", so to speak.