Although this is a bit outside the scope of a normal church web team, if you have individuals with tech backgrounds, or and individual with time to learn and maintain a system, you can create your own online document and file sharing system that will protect the privacy of the content in your files.
The best system for this is to set-up an online web server with the NextCloud system, and then install the Only Office extension. This will give you the ability to share files but also the ability to edit them online - very similar to Office 365 and Google Docs.
NextCloud must be installed on your own online server (we recommend Linode). Someone with basic IT experience should be able to set-up a system within a few hours. Maintenance of the system should be less than 5 hours/month.
Why shouldn't we use Office 365 or Google Docs?
In addition to the cost, Microsoft has had a track record of not protecting privacy with your data files. In addition, they have begun to insert advertisements within the Office 365 interface.
Google Docs are known to be insecure, and they may share the contents of your documents with others.