To support IP-mobility of networks in motion, IETF proposed Network Mobility (NEMO) protocol that uses various signaling messages to ensure connectivity of the mobile nodes with the Internet. However, there has been no comprehensive cost analysis of mobility protocol entities that considers all possible costs. In this paper, we have developed analytical models to estimate total costs of key mobility management entities of NEMO. We have presented numerical results to demonstrate the impact of network size, mobility rate, traffic rate and data volume on these costs. Our cost analysis will thus help network engineers in estimating actual resource requirements for the key entities of the network in future design.