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There was a 2002 study by Meta Group that addressed this issue. Obviously, the numbers may be off somewhat given the fact that a decade has passed since the study was published. They surveyed 63 companies covering a wide spectrum of company size and industries. This study analyzed the total cost of ownership, including professional services, software and hardware costs, from initial installation through the following two years. The range was pretty dramatic, ranging from a low of $400,000 to a high of $300,000,000. That averaged out to $15,000,000 (that may have been the median cost, I'm not certain). Of course it doesn't take too many $300 million figures to skew the figures Average cost for each user worked out to $53,320. As one would expect, the cost of ERP deployment increased in step with the size of the company and number of users. One rule of thumb that I've heard, but have not verified, is that total ERP costs often run about .5 to 1% of revenue.