Actually, I think this is the best antivirus around: http://www.sophos.com/
I used them at my old job. They do all their work with enterprises and education, so I don't know if there is some minimum order that they won't go below (or even if their product can be used in a non-managed, standalone environment), but it might be worth contacting them to see if they can do something for you.

Trials of both NOD and Panda are available so you can try before you buy.

As for suite vs. just antivirus, do you need some functionality that the built-in Windows Firewall doesn't offer?