A shared secret, conference key, must be established among members to securely communicate among them. The Diffie-Hellman is often used for the conference key establishment. In a heterogenous network, the participants have different resources. Therefore, different burden should be placed on different participants. However, most protocols did not address this problem. Wade Trappe et. al. addressed this problem considering the computational power minimization for Perrig protocol. In this paper, we will consider minimization of the cost with considering the transmission since transmission consumes most of the energy. A cost analysis and a minimum cost protocol with or without constraints are presented.