Ask HN: when does your product become overpriced?

I've been following kreci for a while now, on HN and on his blog, and I see he just launched a 20-page book: http://www.kreci.net/android/make-money-on-android/

While I do believe the contents of his book are valuable, are they worth $20 ? I know for most of you it will be hard to appreciate without seeing the actual book, but for me (i have it), it looks like a "buy my book which will teach you how to get rich" scams, written by someone who started to make money out of pure luck, with a less-than-valuable product (iFart stuff).

I know this topic might start some flames, but I believe it's a fair question.