Internet-scale dissemination of streaming contents (e.g., live sports games) can be achieved by infrastructure-based overlay multicast networks, where multicast service providers deliver the contents via dedicated servers strategically placed over the Internet. Given the huge amount of data traffic, one of the major operation costs is the ISP cost for network access. However, existing overlay multicast protocols only consider network performance metrics in building dissemination trees without taking into account the potentially high ISP cost they may incur. This paper presents a scheme, Revenue-driven Overlay Multicast Networks (ROMaN), to assign users to different servers in order to maximize the profit derived from providing multicast services. ROMaN exploits the fact that ISP charging functions are concave by assigning users to the cheapest available servers, and dynamically adjusts the assignment to accommodate the churns of group membership. The evaluation shows that ROMaN not only can reduce ISP cost substantially, but also has shorter end-to-end delay due to smaller overlay size, and the longer a user stays in the group the better the service it will receive.