Cost of a Hardcover Book in 1956.

I was reading sales listings for the book On a Darkling Plain by Clifford Irving. One of the listings mentioned that the price printed on the dustjacket was $3.75. My first thought was how good a deal people received on hardcover books in 1956. Then I remembered that I should take inflation into account. The Federal Reserve Bank of Minneapolis has a Consumer Price Index Calculator on their page. Use it to find what $3.75 in 1956 is worth in 2007 dollars. You will see that a hardcover book was not cheap. The Consumer Price Index Calculator is a good tool for librarians to know about. I have used it to answer several reference questions.