We use Symantec Brightmail Gateways at work, and they're pretty accurate. I don't think using that will be much of a cost savings (probably depends on the licensing agreement with Symantec that a company has). For open source there's a package of ClamAV/SpamAssassin called MailScanner...
LSI makes some RAID controllers that handle many ports, such as this 16 port model:
http://www.lsi.com/products/storagecomponents/Pages/MegaRAIDSAS9280-16i4e.aspx