Now before people start I agree this should be part of the standard Azure Portal, however it isn’t! Therefore if this is something you want then you have two options this portal that you need to configure and manage yourself which I have put the links to resources to get you going. Or you can use https://portal.newsignature.com/ which is another free solution.
Some months ago, a small group within the Developer Experience team began working on a project to enable visibility of Azure usage across multiple subscriptions to keep track of billing as well as to ensure resources weren’t left running after projects and events had finished. The Azure Billing and Subscription Portal was born:
Channel 9 Video on how to configure: