How to Monetize a Database?

I am interested in creating a database app to sell. How can I sell a Creator app by user? For instance, each user is $25 per month. Each database would have a $50 set up fee.

Also, if these are individual instances of the database, how are revisions sent out to all the installs if the master is modified?

Does it make sense to sell individual apps like this or have one master app and sell access to it?