Option A is the recommended approach because the GCP pricing calculator provides the most accurate and efficient means to estimate costs, taking into account the specific usage and pricing of each product involved in the solution. This method ensures the estimate is based on current pricing and detailed usage scenarios. Option B, while useful for organizing data, lacks the dynamic and accurate pricing updates provided by the pricing calculator. Options C and D involve unnecessary provisioning and monitoring for cost estimation, which can lead to inaccurate monthly projections and incur unnecessary charges during the estimation process. For the most reliable and up-to-date cost estimation, leveraging the GCP pricing calculator as outlined in Option A is advised. Reference: GCP Pricing Calculator.