In this paper authors present an ontology framework which is integrated into a tool that supports service intermediaries in the design process of service networks. These networks represent possible instantiations of a value added mashed-up services formed by various decentralized service providers. Based on this, authors provide an application of a path auction with a Vickrey-Clarke-Groves and a Low-Payment-Mechanism to determine the price of mashups. Also, they evaluate proposed mechanisms exploring different graph topologies and bid strategies.