With an enhanced client computer performance and network bandwidth, content distribution services are receiving much attention. However client/server model and peer-to-peer model require vast cost for content distributions. These costs pose an impediment to broaden commercialization of content distribution services via the Internet. Content distribution cost consists of investment for server and network infrastructure which client/server model and peer-to-peer model require respectively. Thus, We focus on network infrastructure, especially in peer-to-peer content distribution networks which drastically increase traffic volume. The main feature of our proposal is utilization of inexpensive inter-ISP connections. This paper presents methods to constitute peer-to-peer content distribution networks that realizes lower cost content distribution and a reduction in the amount of inter-ISP traffic and its costs by considering the priority in usage of ISP interconnections in its distribution. Our proposal extends BitTorrent, which has been widely deployed by several content providers to reduce the load in congested servers and the distribution costs. Our performance evaluations show that our proposal achieves a reduction in network infrastructure costs and improved performance such as distribution time.