A lot of people have thoughfully responded with reasons why this doesn't or can't exist: real-time billing is far too expensive to implement, better to get a huge bill than to lose data or shut down critical systems, etc. I guess it makes sense—ideally you are monitoring your stuff, whether you're using your own tools or built-in ones—and you know ahead of time when your usage is creeping up. Also, I suppose only the customer can really know which systems can be shut down/deallocated to save money and which ones would kill the company if shut down. It sounds like if you're a small startup strapped for resources, you can avoid these bills either by self-hosting or by being careful about how you build your cloud infrastructure. I.e. maybe you could host your app on your own box OR on an equivalent VM in Azure that's just going to fail if it runs out of disk/CPU/outgoing bandwidth instead of autoscaling to outrageous levels.
