You can opt for the Pay Per Use agreement for the extra usage bill as a trigger or knowing that you will be getting the invoice at the end of the month.

For SkyConnect, you can schedule a monthly activity to check the users provisioned on the domain are in use, what is the storage used, have you implemented the quota. 

For Vaultastic, you can review people accessing the Vaults frequently? Or do I need back up plan only? Can this data be moved to S3? 

So these reviews and checks have to be done at your end, which will help you plan better in the subsequent months.