From Joel Snyder’s “Exchange: Should I stay or should I go?” (Network World: 9 March 2009):
There are many ways to buy Exchange, depending on how many users you need, but the short answer is that none of them cost less than about $75 per user and can run up to $140 per user for the bundles that include Exchange and Windows Server and user licenses for both of those as well as Forefront, Microsoft’s antispam/antivirus service. …
If you really want to make a case for cost, you could also claim that Exchange requires a $90 Outlook license for each user, a Windows XP or Vista license for each user, and more expensive hardware than a similar open source platform might require.