AWS Organizations is the best fit because it providesaccount-level isolationandconsolidated billingacross member accounts. AWS documentation states that the management account receives a single bill that combines usage from all member accounts, which directly supports a consolidated monthly chargeback view. Creating a member account per business unit also satisfies the isolation requirement better than sharing one account with tags. Separate organizations per unit would add unnecessary overhead and remove the simplicity of a single consolidated management structure. Therefore, a single AWS Organization with one member account per business unit is the cleanest and lowest-overhead design. (docs.aws.amazon.com)

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