Very often it so happens that the cost of operating an Intrusion Detection System (IDS) exceeds the cost of purchasing the IDS itself. In such cases, regular operation and maintenance of the system becomes expensive. Thus, it becomes essential to reduce the operating cost of the IDS without compromising on the performance and reliability of the IDS. Apart from the initial cost of procuring the IDS, other costs include cost of accessories required and cost of administration etc. In this paper, the authors calculate the cost benefit tradeoffs of an IDS. They propose a method to determine the optimum operating point of the IDS.