Typical solutions for Web services composition problem develop a single intermediary which mediates or choreographs computation and communication among the existing services to realize a target/goal service. However, such a centralized choreography mechanism can involve communication/computation overhead that can be reduced through its decentralized realization. With this as motivation, we study the problem of synthesizing a decentralized choreography strategy that will have an optimum overhead for service composition by developing a set of site-specific choreographers working concurrently to implement a desired goal service. Each communication/computation is quantified by a cost. We develop an algorithm that takes as input the existing services, the goal service, the costs and produces as an output a set of site-specific choreographers that optimally realize the goal service using the existing services. The contribution lies in the formulation of the optimal decentralized choreographer synthesis problem as well as its solution and extends our earlier work in two ways: decentralization of solution and its optimality.