The unique wide-area surveillance capability of UAVs has led to their increasing use in environmental search tasks. This paper studies the use of SUAVs to assist UAVs in collaborative searches, aiming to expand the search area of UAVs while reducing search costs. Considering practical constraints such as UAV endurance, fuel consumption, and cost of detection sensor, a mathematical optimization model is constructed to minimize the whole costs. The mathematical problem is NP-hard, and an optimization algorithm is proposed to solve the problem. Simulation experiments demonstrate that the proposed algorithm can effectively reduce costs compared to conventional algorithms, and the computation time of the algorithm is significantly shorter than that of conventional algorithms.