You receive value from consumption of the book.
Have a mechanism for ebooks where you pay a much smaller fee when buying the book (maybe $3 of the total price of $10 for the book), then only micro-pay for pages you actually read in that book up to the whole price of the book.
A different way to monetize your content.
A free content website where you can pay as you like for the content you like to pay for. To make micropayments, you pre-purchase site credits for fixed amounts ($1 for 100 credits, $5 for 600 credits, etc.), and you can spend these on articles you enjoyed by simply filling in the right amount on the content page. Each content page also shows how many credits it has earned from visitors.
As a good measurement of what was the right answer.
Allow users to donate how much they want (maybe even less than 1 dollar cent), based on their satisfaction of the result they got in the SERP. This will give a better indication as to what is a really useful answer to a specific query.