Best way to prevent that is to set an account billing alert that will SMS you if your bill goes over $X dollars. I doubt this feature will ever be implemented,

Best way to prevent that is to set an account billing alert that will SMS you if your bill goes over $X dollars. I doubt this feature will ever be implemented, as trying to provide some kind of real-time spend is extremely hard, especially when there are 100+ service bills that need to be aggregated, which usually is a batch process where these things get resolved.