Hello Ahmed,

OAC can be bought in 2 ways:

   -By number of users as a separate cloud subscription (not Universal Credits): this way is only available for expansion of existing customers

   -By number of users using Universal Credits (the normal way since a while to use any IaaS and PaaS of Oracle Cloud)

   -By OCPUs using Universal Credits.

In any of the cases above the price is clear in advance and shouldn't vary.

E.g. if a customer need 20 users of OAC and create an instance of OAC 20 users (number of users specified in the instance creation). That instance will consume the same universal credits every month.

The same happens with OCPUs.

The only scenario when the consumption would vary is if the customer uses OAC OCPUs and start/stop the instance (e.g. starting it in the morning and stopping it at nights and weekends) as well as if they  scale up/down the OAC instance during certain hours. In this case the consumption of cloud credits would vary and it would make sense to have some control.

In general for any IaaS/PaaS of Oracle in OCI you can use budgets and alerts very easily to be notified when a % of the budget is being reached.

Here you have the details:

https://docs.cloud.oracle.com/en-us/iaas/Content/Billing/Tasks/managingalertrules.htm

You could e.g. have OAC in an OCI compartment or use an specific OCI tag for it so you only take into account OAC for the budget % alert.

Hope it helps!

Juan Diego