I happened to do some searching on A History of Us today, and noticed 3rd party sellers are over-charging for it. This happens quite frequently on Amazon, as people selling on Amazon hope to find someone not paying attention.
Please don't pay more than you have to. The retail price is 41.57. While I am a bit uncomfortable with this high price, it is the most you should pay at Amazon, Barnes & Noble, Lulu, and other reputable sellers. If you see anyone charging any more, please feel free to continue looking around for a better price.
Update (3 Aug 2023):
The copyright notice for this book is the Creative Commons Attribution Non-Commercial-ShareAlike 4.0 International License. One of the provisions of that license is that no profit is allowed from the sale of the book, nor can the material in it be used in another publication that is for sale. In short, no one can profit from my work in any way. This makes sales at an increased price a violation of the copyright. I have begun sending copyright infringement notices to online sellers who charge more than the publication cost.
Please purchase from Lulu.com (best), Barnes and Noble (better) or Amazon (not a reseller on Amazon), all three of which adhere to the copyright notice.