[AngusH]

If the amount of storage that you can use is limited by quota (say 50GB) the problem becomes relatively easier.

You set a quota for 50GB of storage and no more. The server then restricts you by disk quota to that amount of storage.

The cost is then calculated as 1.15USD per month.

So you don't pay more than 1.15 per month.

Compute and transfer (and other things) could be covered by separate similar quotas with a single maximum spend figure at the bottom of the table.