What is the best way to collaborate on documents in a group?

Assume there are 100 or so documents and a group of 10 remote collaborators that will grow to 200 documents and 20 collaborators over the year.  When a new collaborator is added it would be helpful not to have to manually add privileges for each of the documents.  Also, this is for a non-profit with a limited IT budget, so use of Google Docs or something similar is preferred.