In some harsh environments, manually deploying sensors is impossible. Alternative methods may lead to imprecise placement resulting in coverage holes. To provide the required high coverage in these situations, we propose to deploy sensor networks composed of a mixture of mobile and static sensors in which mobile sensors can move from dense areas to sparse areas to improve the overall coverage. This paper presents a bidding protocol to assist the movement of mobile sensors. In the protocol, static sensors detect coverage holes locally by using Voronoi diagrams, and bid for mobile sensors based on the size of the detected hole. Mobile sensors choose coverage holes to heal based on the bid. Simulation results show that our algorithm provides suitable tradeoff between coverage and sensor cost.