This paper presents a structured and systematic approach to implementing lean in-plant logistics complemented by a cost model. It delves deeply into chronic losses and inefficiencies in manufacturing plants, emphasizing issues in material flow, line stoppages, productivity, inventory levels, line-side storage, and kitting, impacting higher costs. Each process phase is meticulously described, along with the inputs derived from them. Organizations benefit from reduced costs, waste elimination, and increased productivity by adopting lean in-plant logistics. The detailed steps outlined in each phase guide practitioners in addressing all aspects of logistics operations within the plant, enabling comprehensive optimization and lean implementation. The proposed system offers numerous advantages, including decreased inventory levels, more efficient line-side inventory management, and lower overall costs.