Disk based storage systems serving continuous media content are evaluated using metrics such as startup latency, buffer size, and the number of concurrent streams. The design of a practical system must evaluate the tradeoffs among these parameters to achieve a target system performance while minimizing operational costs. In this paper, we describe a generic model that can be used for characterizing the performance of disk based storage systems. We subsequently develop a formulation that relates the performance of the storage system to the cost of implementation. The model is evaluated using current disk and memory prices to determine the cost per unit bandwidth and cost per session and evaluate the best operating point for a given session bandwidth and latency requirement. The results demonstrate the utility of the proposed method in designing video servers. We believe this technique to be essential to evaluate the feasibility of building economical storage architectures.