Talk to the people who wrote the first book on Meteor.js. I know they pulled in over $500k.

That's probably a unique case because in the beginning the documentation was so bad, but especially in new and esoteric programming languages/methods $50 is no big deal, and there are lots of willing buyers. I'd bet the HaskellBook authors pulled in 100k+ too.

Adam Wathan (PHP + Laravel stuff) had a $100k book launch - http://www.productpeople.tv/81

I know a half dozen other authors of technical/programming books who have probably made between $50k to $100k over the life of their books.

I wouldn't be so sure. Programming has a distinct advantage: people can make money from programming skills. And also, people can save money on programming costs if a book teaches them/their programmer enough knowledge that outside talent isn't required.

So there's a lot more money potential for the average programming book than there is for the average novel. (Bestselling novels make much more, but only a few books get that status)

The thing about business/education/training books is that they don't have to be priced like conventional non-fiction books. You sell them on the value they provide.

If you give me a system that will help me become a full-time programmer in 12 months, making $75/hour, then I'll gladly give you hundreds of dollars for the book.

Out of 100, at least 3 people will see that value. If you charge $50/month for the book/course, and have a list of 3,000 people, you are effectively looking at a full-time income