It's ironic that a book on Economics and the "free market" should somehow be criticized for not being priced at this magical mystical $9.99 that hordes of Kindle users think should be the one price for all Kindle books. If $23 is too much for you, then DON'T BUY IT. As for me, I own two Kindles. I don't want another hardcover book on my bookshelf. So I will gladly pay the $23.
You are paying for the content. As such, you get to decide how you want it. Personally, I would recommend doing what you probably do with most other purchasing decisions, and decide on an ebook by ebook basis. Of course, I tend to also find the prices of paper versions irrelevant, as I prefer the Kindle version. I have not purchased a paper book in months.