The company will run multiple workloads for different business units and wants to separate and track costs for each unit with the least operational overhead. Which solution meets this requirement?

Creating a separate AWS account for each business unit within AWS Organizations is the most effective solution. AWS Organizations allows you to centrally manage and consolidate billing for multiple accounts, naturally separating costs by account. This approach provides strong isolation for resources and permissions, simplifying cost allocation and tracking with minimal operational overhead. Each business unit can operate independently within its own account, and you can apply policies and track spending at the account level. Maintaining a spreadsheet is a manual, error-prone, and high-overhead solution that doesn't integrate with AWS billing. Storing cost data in DynamoDB would require custom development and significant operational effort to extract, process, and store billing information, which is not natively supported for cost tracking. The AWS Billing console provides overall billing information but does not offer a native mechanism to assign resource owners or track costs at a granular, business-unit level without the underlying account structure provided by Organizations.