A company is running workloads for multiple departments within a single VPC.

Adding a department tag to each resource and configuring cost allocation tags is an action that can help you accomplish the goal of billing each department for its resource usage with the least operational overhead. Tags are simple labels consisting of a key and an optional value that you can assign to AWS resources. You can use tags to organize your resources and track your AWS costs ona detailed level. Cost allocation tags enable you to track your AWS costs on a detailed level. After you activate cost allocation tags, AWS uses the cost allocation tags to organize your resource costs on your cost allocation report, to make it easier for you to categorize and track your AWS costs2. Moving each department resource to its own VPC or its own AWS account is an action that can help you isolate and control the resources for each department, but it would incur more operational overhead than using tags. Using AWS Organizations to get a billing report for each department is an action that can help you consolidate billing and payment across multiple AWS accounts, but it would not help you bill each department for its resource usage within a single VPC.