The correct answer is D, AWS Pricing Calculator. This tool allows users to estimate the cost of running resources, services, and applications in different AWS Regions. By inputting the required resources and configurations for their application, the company can compare the costs of running it in various AWS Regions and identify the most cost-effective options. The other options, A (Cost Explorer), B (AWS Budgets), and C (AWS Trusted Advisor), are useful for managing and optimizing costs after deployment but do not provide the pre-deployment cost estimation needed in this scenario.