[mark_l_watson]

I would take the authors at their word and pay just what you are comfortable paying.

Variable pricing is really an interesting business model. I have three books for sale on leanpub, each with a suggested price of $6 with a minimum of $4. A lot of people pay more than $6, BTW, the most so far that anyone has paid is $50. Payments in the $10 to $12 range are common, but probably less than 15% of sales.