Companies with a wide range of variety on the markets have to reduce their internal variety for reducing their costs. This can be reached through modular product families, where more than one concept is possible. A decision making based on costs is missing for the choice of the developed concepts. In this Paper an approach for developing modular product structure concepts based on cost is presented. Based on literature review the Integrated PKT-Approach for developing modular product families is adapted for analyze cost, process and product structure for developing and cost prognosis of concepts and modified tools for analyzing cost are explained. This approach is used in a case study for an industry company where three cost-efficient variety optimized concepts were developed. The approach is helpful for developing cost-reduced concepts based on cost analyses and gives a cost prognosis for rating the concepts.