Whoa, just researched this, and it turns out that Oz does have money in the first book (kids in the Emerald City pay for green candy with green pennies etc.): it’s sometime later in the series that Oz becomes essentially Communist. See this description from the 6th book in the series, The Emerald City of Oz: http://www.gutenberg.org/files/517/517-h/517-h.htm

“No disease of any sort was ever known among the Ozites, and so no one ever died unless he met with an accident that prevented him from living. This happened very seldom, indeed. There were no poor people in the Land of Oz, because there was no such thing as money, and all property of every sort belonged to the Ruler. The people were her children, and she cared for them. Each person was given freely by his neighbors whatever he required for his use, which is as much as any one may reasonably desire. Some tilled the lands and raised great crops of grain, which was divided equally among the entire population, so that all had enough. There were many tailors and dressmakers and shoemakers and the like, who made things that any who desired them might wear. Likewise there were jewelers who made ornaments for the person, which pleased and beautified the people, and these ornaments also were free to those who asked for them. Each man and woman, no matter what he or she produced for the good of the community, was supplied by the neighbors with food and clothing and a house and furniture and ornaments and games. If by chance the supply ever ran short, more was taken from the great storehouses of the Ruler, which were afterward filled up again when there was more of any article than the people needed.”