Use free AVG all the time on single PC's and works great.
Tried to install on Windows Server, but will not install as the free edition only works on single PC's. Can purchase the Server AVG version if necessary.
Is there any comparable free antivirus software out there that runs on a Windows server?
Runner.
You could try anti vir from Avira. Brilliant on desktops. Not sure as to whether it will work on a Sever. Download and try I suppose! http://www.free-av.com/
The commercial avg is great and not too expensive, one of the cheaper ones. Surely this could not be an impediment to you considering you the the free HOME version all the time.