Taking a quick poll here - how much would everyone be willing to pay for this?
After that it would be ideal to charge a little ($5/month) for the next 2-3 users, and more for larger teams. Ofcourse, give more features as the team sizes grow.
Note that your market is larger than a CRM.
Then scale a lot for larger groups/companies. Something like the atlassian pricing tiers?
There is a large government market to hit also.