A company runs applications on Amazon EC2 and periodically assesses AWS costs. The company recently identified unusual spending and needs a solution to prevent it. The solution must monitor costs and notify stakeholders of unusual spending. Which solution meets these requirements?

AWS Cost Anomaly Detection is specifically designed to monitor your AWS costs using machine learning, identify unusual spending patterns, and notify stakeholders. This directly addresses the requirement to prevent unusual spending by detecting it early. Using an AWS Budgets template for a zero-spend budget is for ensuring no spending occurs, which is not the same as detecting unusual spending on active resources. AWS Pricing Calculator estimates are for planning future costs, not for monitoring current spending or detecting anomalies. Amazon CloudWatch can monitor various metrics, but it doesn't inherently have the machine learning capabilities of Cost Anomaly Detection to identify cost anomalies without significant custom configuration, which is less efficient than the purpose-built service.