Which AWS service allows you to set custom cost budgets and receive alerts when costs exceed thresholds?

Correct answer: AWS Budgets

Option C is correct because AWS Budgets is the dedicated service for setting custom cost and usage budgets, with the ability to send alerts via email or Amazon SNS when actual or forecasted costs exceed defined thresholds. Option A is wrong because AWS Pricing Calculator is a planning tool used to estimate costs for new workloads before deployment, and it does not monitor actual spending or send budget alerts. Option B is incorrect because Amazon CloudWatch is a monitoring and observability service for infrastructure metrics and logs; while it can track billing metrics with some configuration, it is not the primary or purpose-built tool for cost budgeting and threshold alerts. Option D is wrong because AWS Cost Explorer is an analytical tool for visualizing and understanding historical cost trends, not for setting forward-looking budget limits and triggering alerts.