Which solution is the MOST scalable and cost-effective way to meet these requirements?

Explanations:

While Amazon EMR can analyze large datasets, using Kinesis for this purpose is not cost-effective and adds unnecessary complexity, especially for monthly reports. It would require continuous streaming infrastructure that may not be fully utilized.

Enabling Cost and Usage Reports in the management account and delivering them to Amazon S3 is a scalable and cost-effective solution. Amazon Athena allows for serverless SQL queries directly on the S3 data, making it easy to analyze the costs without provisioning additional resources. This solution aligns well with the requirement to run monthly queries.

Enabling Cost and Usage Reports for member accounts complicates the architecture by requiring configuration across all accounts. Although Redshift can handle large data analytics, it incurs more costs and management overhead compared to using S3 and Athena.

Using Kinesis to deliver Cost and Usage Reports adds unnecessary complexity and cost. QuickSight is useful for visualization but relies on processed data, which would be less efficient compared to direct queries via Athena on S3. Additionally, this option does not utilize a simple and cost-effective monthly reporting strategy.