This paper studies the event-triggered consensus for mobile sensor networks (MSNs) under a given energy budge. Based on real-time communication among neighboring sensors, an event-triggered scheme is used to determine when the control update will be executed. By proposing a consensus protocol under such an event-triggered scheme, the consensus problem of MSNs with the guaranteed cost is addressed, where a global linear quadratic cost which involves the cost for communication and control input is introduced as the performance measure of energy cost. By performing the system order reduction, the event-triggered consensus problem can be transformed into the stabilization problem of the system with the guaranteed cost. A sufficient condition on event-triggered average consensus of MSNs can be derived. A computational algorithm which minimizes the cost bound is presented to calculate the controller gain matrix and event-triggered weight matrix. A simulation example is given to illustrate the theoretical results.