With the advent of the Internet of Everything, the forthcoming 6G networks will necessitate an extensive deployment of base stations to achieve comprehensive network coverage. This development presents a formidable challenge for operators due to the surging expenses associated with each base station and the exponential increase in their quantity. Consequently, formulating strategies to mitigate network deployment costs has become an imperative challenge that operators must address urgently. The fully-decoupled radio access network (FD-RAN), through its innovative separation of uplink and downlink base stations, provides the flexibility for deployment in response to asymmetrical service demands, offering a promising solution to the deployment cost dilemma. In this study, we first propose a techno-economic cost model (TECM) for FD-RAN deployment based on the techno-economic approach and then formulate a cost-minimization problem for decoupled network deployment. To tackle the complexity of massive terminals, we present an adjacent gravity-based optimal link clustering algorithm (AGOC) to transform the significant 0–1 programming problem into a mixed integer program. Leveraging FD-RAN's uplink-downlink decoupling, we decompose the original problem into separate subproblems for uplink and downlink network deployments. For the decoupled problem, we further propose a branch-and-cut based network deployment (BCND) algorithm to solve the two decoupled deployment subproblems, respectively. Simulation results indicate that FD-RANs can offer significant cost benefits when facing differentiated service demands. Furthermore, the analysis reveals that power consumption and rental costs are the primary factors influencing network expenses.