In this paper, we address the problem of multimedia streaming over DiffServ networks that offer various qualities of service (QoS) at different price points. In particular, we seek cost-distortion optimized transmission policies that minimize the distortion seen by the client under a cost constraint. Our results show that for ondemand streaming of stored media, DiffServ networks provide little or no gain over networks that offers only a single, cost-effective, QoS. However, for real-time conversational communication or multicast streaming, optimized transmission over DiffServ networks can perform better than optimized transmission over any single QoS by over 2 dB at the same cost.