Cellus

At the moment I would not recommend COMODO Antivirus. There are many other AV products out there with far superior detection rates and capabilities. Many of the major and popular brand AV companies provide discounts for non-profit and educational organizations, so if you meet their requirements, contact them to see if you can get in on it. I know there can be some significant budget constraints, so take a look.

Addendum: If you can not find information on the AV company websites, phone or e-mail them. Sometimes either the information is either really deep on the website, or they do not publicly publish the information - either way they can support non-profit and/or educational organizations. I know, for example, Trend Micro has non-profit licensing pricing. Other AV companies may as well.