AntiGen is a great set of products for providing security technologies.  Some of these come in very price competative and feature rich. For example, for spam, smtp and a/v filtering the US price is $1.25 per user per month.

For more info see below

Microsoft Releases Antigen E-Mail Security Products http://go.microsoft.com/?linkid=5049691

On June 6, Microsoft announced the release of Microsoft Antigen e-mail security products -- including Antigen for Exchange, Antigen for SMTP Gateways, Antigen Spam Manager, and Antigen Enterprise Manager -- available to customers July 1, 2006. Microsoft Antigen products help business protect their Exchange, Windows-based SMTP gateway, Live Communications Server, and SharePoint servers from viruses, worms, spam, and inappropriate content. Read about new product features http://go.microsoft.com/?linkid=5049723  or download the new 90-day trials http://go.microsoft.com/?linkid=5049724  to see how Antigen can help protect your messaging and collaboration servers.

ttfn

David