One of the costs associated with ECM, particularly with commercial ECM, is the 3rd party software they rely upon to function. There are a whole host of such software to be concerned with:

• Operating Systems: It is unlikely that any company seriously looking at ECM currently utilizes free operating systems -- the vast majority will be using a Microsoft product (ranging in price from a couple hundred to over a thousand dollars depending on the flavour), even if they are looking at a Linux variant the chances are very good that they will use one of the commercially available versions like Red Hat or SUSE. Over three years most will see costs for OS to be around $500/year
• Database: This is sometimes a whopper, sometimes a mid-range cost, and sometimes it is entirely free. The truth is, however, that any corporation TRULY NEEDING an ECM program because the lack of a program is hurting the company (the bane of large corporations and the price of success) will likely find that they need to spend significant money on a commercial relational database management system (RDBMS) ... likely the grandaddy of databases, Oracle. Databases are usually licensed for use on a particular class of computer server (ie: with "X" cpus) and at a pure-back of the envelope calc could be measured at about $10,000/year/cpu
• Web or Application Server: While Internet Information Server (IIS) is well entrenched, the free apache web server still rules the day and you will find few corporations that will pay directly for a web server. J2EE Application Servers, on the other hand, are frequently licensed by corporations and can themselves be quite dear (especially when compared to free), often coming in at about the same cost as an OS or $500/year/server
• SNMP and related monitoring software -- for server and service health monitoring. This is a varied field, from "free" to about $1,000/server/year and everywhere in between.
• DNS, SMTP, POP3, NTP, SSH, FTP: these necessary network services are typically provided by the Operating System at no extra cost

Often these costs are "assumed" and not calculated or shared by other applications and servers and not then accounted for. Overall they could account for as much as 5% of the total cost of ownership (or as little as zero).