You can also rate limit some APIs.
https://cloud.google.com/billing/docs/how-to/notify#cap_disa...
> You might cap costs because you have a hard limit on how much money you can spend on Google Cloud. This is typical for students, researchers, or developers working in sandbox environments. In these cases you want to stop the spending and might be willing to shutdown all your Google Cloud services and usage when your budget limit is reached.