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Not sure, haven't gotten to that yet. Just from looking at the prices of other PragProg books somewhere around $21.95-24.95.

Is it still worth (materialistically) writing a book considering (see PRICING section) http://fabiensanglard.net/gebbdoom/ ?

I'm not doing it for the money. Writing a worthwhile book is about the least efficient way to make money.

Not sure about how least efficient though, indirectly it will help a lot I believe.