Why do none of these cloud services have spend caps?
Why not have a simple "budget" setting and have a setting what to discuss when it's exceeded. Options could be "shut down most recently started resources" or "shut down everything but don't delete any data", and "delete everything".
Azure has this in their Cost Management page, available for each subscription. You can set a budget and get notifications about when you are reaching its limit. Not sure about the power it has with re to shutting things down.
I believe you can hook into apis to shut things down, but it’s not super straight forward.
There are many Azure services that can’t be set to zero dollar billing without data loss, so I’m not sure how Azure could deal with those in a unified manner.
Why not have a simple "budget" setting and have a setting what to discuss when it's exceeded. Options could be "shut down most recently started resources" or "shut down everything but don't delete any data", and "delete everything".