I work for 5 catholic churches and have avast on all of them.
We use the professional "netclient" editions and have paid for the licensing. The 50% off is a pretty good deal for what you get. Even better is the additional percentage off when you renew (I believe it's another 15%).
Regardless if you're a church or not, you're still conducting business with your computers. Scheduling masses, counting contributions, creating cemetery maps, etc. All of that is part of what makes your church money, which is a business.
You can use the "free" edition, but it's still basically stealing. A good Christian / Church wouldn't do that now, would they?