For example, "Four Essays on Philosophy" is indeed a cornerstone of Mao's work, but Amazon sells it for $22.50. It should be available for $5 tops. Try in a used book store.
Quotations from Chairman Mao Tse Tung is more correctly priced at $9.50. That is the book that over a billion people have. It's what people mean when they say "Mao's little red book." Broken into short little snippets, it may be good for weak readers. We prefer that students study the works that the quotations come from, in whole and in their context, but we understand why people want this book for history's sake.
On Guerrilla Warfare is another impotant area of Mao's work. Mao's military writings explain why technologically and financially superior opponents lose to proletarian-led People's War.
Selected Readings from the Works of Mao...
The above choices come under the name "Mao Tse-tung." Recently, the romanized version of Chinese is "Mao Zedong."