A company wants to experiment with individual AWS accounts for its engineer team. The company wants to be notified as soon as the Amazon EC2 instance usage for a given month exceeds a specific threshold for each account. What should a solutions architect do to meet this requirement MOST cost-effectively?

AWS Budgets is the most cost-effective and direct solution for this requirement. It allows you to set custom budgets to track your costs and usage, including specific services like EC2, and receive alerts when thresholds are exceeded. Setting a monthly budget scoped to EC2 instances for each account, with SNS notifications, directly addresses the need for timely alerts on EC2 usage exceeding a monthly threshold. Using Cost Explorer reports with SES notifications is less ideal because Cost Explorer is primarily for analysis and visualization; while it can send reports, its primary function isn't real-time budget alerting. AWS Cost and Usage Reports (CUR) with Athena and EventBridge is a powerful, highly granular solution, but it's significantly more complex and thus less cost-effective for this specific, straightforward budgeting requirement. It involves more services and setup, increasing operational overhead.