This study investigates a multi-echelon supply chain consisting of two suppliers, a manufacturing plant, a distribution center, and a retailer. In the manufacturing plant, two raw materials are used to produce one finished product, and these two raw materials are processed in the preparation machine before entering production. This supply chain incorporates two distinct customer classes: high-value customers with high lost sales costs and regular customers with lower costs. To manage these differences, stock rationing strategies prioritize high-value customers, potentially rejecting regular orders to reserve inventory for anticipated high-value demand. Material flow between the stages in the supply chain is driven by reorder point/order quantity inventory control policies, ensuring timely replenishment and stock availability. The model evaluates key performance metrics, primarily focusing on long-term average cost as a comprehensive system efficiency measure. This includes holding costs for storing inventory, production start-up costs for initiating the production process, ordering costs for placing orders, lost sales penalties for unmet demand, and backordering penalties for delayed orders. Validated through simulation, the model ensures robust performance metrics accurately representing the supply chain's dynamics. The study includes parameters for inventory rationing policies that emphasize prioritizing high-value customers. Combining customer prioritization and comprehensive cost assessments aims to improve supply chain performance and efficiency. The study provides a holistic approach to supply chain operations by addressing inventory management and customer service levels.