The correct service for defining and tracking expenditure and utilization against budget thresholds is the one specifically dedicated to this purpose, providing alerting capabilities when spending exceeds or is anticipated to exceed the predefined limits. AWS Cost Explorer is useful for visualizing spending patterns but does not include alerting functions based on thresholds. The tool that allows for detailed billing reports is integral for analysis but is not designed for real-time alerting. Lastly, the service used for initial cost estimates does not track actual spending against budgets post-deployment.