Along with the speedy increase of cellular traffic due to new generation mobile devices, cellular network operators have been looking forward to offloading cellular traffic through WiFi networks. However, it is practically hard to satisfy both the operators and users in considering the poor coverage of current WiFi networks. Instead, WiFi tethering, which is a different way to provide WiFi networks, can solve this problem sufficiently and achieve mobile data offloading. This paper proposes a mobile tethering-based cooperative network which can make heterogeneous users gain certain profits after they participated in it. In the first stage of our system, each user's cellular traffic demand is allocated to others as a way which can minimize the total cellular traffic cost. According to this optimal resource allocation, the tethering price can be determined in the direction of maximizing total utility of all the participated users. Through the simulation results, we observed the reduction of total cellular traffic cost and found various optimal tethering prices in terms of different traffic demands. Although we made some assumptions in order to simplify our system model, it can be verified that it may also show an excellent performance in practice.