Back Ground:
I come from a company of 5K users spread across a large campus with several remote sites. We have had various worms intrude on our day to day activities. Without anything other than up to date anti-virus and some simple PIX type configurations it has been unpleasant.
Time cost:
One attack slowing Internet traffic to a crawl.
Manpower: 2-3 Network 2-3 Data fairly dedicated over the course of a few days. Do the math for the cost of 6 senior people finding and cleaning infected machines.
Quotes todate to implement a NIDS solution that encompasses external, DMZ, internal, server farms, 6 mid range devices 100K.
Quotes on HIDS solutions vary as per desktop and server but basically you are looking at 1-2K per server and 50-80 dollars per desktop licence.
Kim