In recent years, wireless sensor and actor networks (WSANs) have been extensively deployed to monitor physical environment and facilitate decision making based on data collected. Emerging applications such as road surveillance highlight some interesting research issues in WSANs, including coordination problems in sensor-actor or actor-actor communications. In this paper, the issue of choosing a set of working actors for coordinating data transmission in a road sensor and actor network with minimum communication cost is studied. A theoretical model is introduced to analyze the communication cost of data transmission in WSANs, and the sensor-actor coordination problem is formulated as an optimization problem. It is demonstrated that the problem can be divided into subproblems, and optimal solutions can be obtained by using a dynamic programming algorithm. A novel graph-based algorithm is also proposed with a communication-cost graph used to depict the cost of data transmission and a modified Dijkstra's algorithm to find optimal solutions in reduced time complexity. The efficiency of the proposed algorithms is confirmed using extensive simulations.