Aircraft design and manufacturing represent a complex, large-scale systems engineering endeavor involving multiple disciplines and processes. In recent years, the rapid advancement of electrification and digitalization technologies has significantly increased design complexity, revealing limitations in cost control and requirements management within traditional design approaches. This paper proposes a novel design methodology that integrates Design-to-Cost (DtC) principles with the Requirements-Functional-Logical-Physical (RFLP) framework, using an electric propulsion fixed-wing airliner as a case study. The method incorporates DtC principles into the Functional phase of the RFLP process, decomposing total cost into sub-cost components while ensuring compliance with requirements to achieve cost-constrained optimization. Results from the case study demonstrate significant improvements in design process transparency, cost control efficiency, and cross-disciplinary coordination. The paper concludes with a discussion of limitations and directions for future research.