Rapid growth in mobile data traffic and technological improvements in mobile devices revealed the concept of collaborative Internet access via User Provided Networks (UPN). According to this approach, users with strong cellular connection share their own connections with other users that have limited or no cellular connection. However, in such services, one of the key issues is the users' willingness to contribute. In this study, we propose a novel incentive mechanism based on Rubinstein's sequential bargaining model. In the proposed scheme, incentives are given by the mobile network operator as virtual currencies, according to the bargaining of users and experienced quality of service. Decisions of users for requesting or offering UPN services depend on energy cost and utility estimations according to the actual communication signal parameters. For this purpose, we introduce realistic energy consumption and data rate models after performing extensive set of experiments and applying various regression methods. We implement the proposed system in a real environment and show its effectiveness in various scenarios.