This problem should be solved with a simple form in the billing area, not a solution that probably requires upwards of 40h of work to set up and properly test t

This problem should be solved with a simple form in the billing area, not a solution that probably requires upwards of 40h of work to set up and properly test to a level I would trust it with anything. Even then it's dependent on delayed cost reporting with unknown failure modes. It merely makes a best-effort at containing the costs and it doesn't actually limit them.