In the recent past, the focus of engineering design has evidently shifted from product performance to cost-effectiveness and there has been a growing awareness of the need to integrate all engineering resources to realize economically optimal solutions. Despite being the primary motive of the emerging design philosophy, estimation of cost during design process and its incorporation in numerical optimization of design remain less explored. The thesis aims to address the issues pertaining to optimization of broadly integrated design problems with a focus on cost-modeling for design and its deployment in the optimization process. A comparison of the performance-oriented and cost-driven design approaches leads to a novel, unified approach termed design-for-integrated-cost-and-performance. Various cost-modeling methodologies as applicable to engineering design are studied and their applications in structural engineering are used to validate the above arguments.