One of the most often-cited studies of the total cost of ownership (TCO) of ERP was completed by Meta Group in 2002. (Gartner acquired Meta Group in 2005.) This TCO study accounted for hardware, software, professional services and internal staff costs. Costs included initial installation and the two-year period that followed, which is when the real costs of maintaining, upgrading and optimizing the system for your business are felt. Among the 63 companies surveyed--including small, medium and large companies in a range of industries--the average TCO was $15m (the highest was $300m and lowest was $400,000). While it's hard to draw a solid number from that kind of range of companies and ERP efforts, Meta came up with one statistic that proves that ERP is expensive no matter what kind of company is using it. The TCO for a "heads-down" user over that period was a staggering $53,320.
Source: CIO, http://cio.com