maby worth trying a polite official email (use the org's email if they have one ) to AVG explain the situation and that its a non profit org and that you would like to use AVG on just 10 machines but cannot afford a business licence .... see what they have to say !?
you never know they may allow you to use the free version on all 10 machines as you are none profit or at least maby be able to offer a discounted package
you could also try emailing the other anti virus makers too
avast is a good anti virus too along with nod32