Here they are, in summary. We need not buy modems. We could work out a full package for internet and tunnelling access. Then we would house the system at one of the group's buildings in exchange for setting up a Local Area Network and a little extra cash. Every other organization's users would connect via modem.
Software is a minimal cost relatively speaking.
But you have to figure on some expenses for security, etc. Staffing is an important issue. Cost would decline after that. How does this work out. Let's take a synagogue with a membership of 200 families as an example.