Tip: Setting a budget does not automatically cap Google Cloud or Google Maps Platform usage. The default behavior of budgets is to trigger alert emails to Billing Account Administrators so that you know how your usage costs are trending over time. Budget alerts prompt you to take action to control your costs, but do not automatically prevent the use or billing of your services when the budget is met or exceeded.
One option to cap spending is to use budget notifications to programmatically disable Cloud Billing on a project. -- cloud.google.com/billing/docs/how-...
It seems that you can Shutdown on alert,