In this paper, we provide a cost optimized algorithm to design a real-time data transmission network architecture and realize real-time monitoring of transmission line in smart grid. How to deliver this real-time data to the control center efficiently is a critical challenge to build an intelligent smart grid. We formulate a three-layer network structure that can provide cost effective data transmission by the meantime, the bandwidth, delay, and connectivity constraints can be well met. Furthermore, the optimal placement of the LTE transceivers is studied aiming at maximizing the bandwidth and minimizing the delay in information delivery. The results we present in the paper individually analyze the effect of variation in each of the constraint on the cost of the network while other constraints are assumed to take up average values. Our analysis shows that three-layer wireless network used in smart grids can solve the problem of real-time data transmission and reduce the overall cost of transmission line monitoring network by the algorithm proposed in this paper.