This study investigates cost management strategies in government infrastructure projects by analyzing the structure of direct and indirect costs and proposing a lifecycle-based approach to enhance fiscal efficiency. The framework includes four key measures: (1) allocating 15%-20% contingency reserves during planning, (2) incorporating cost-performance evaluation weights in bidding processes, (3) deploying digital monitoring systems for real-time construction oversight, and (4) implementing predictive maintenance models for operational cost control. Through a case study of Beijing Daxing International Airport, the research demonstrates how integrated lifecycle management optimizes resource allocation and improves cost-effectiveness. The findings highlight three actionable recommendations: intensifying risk assessment protocols, leveraging emerging technologies like BIM and AI analytics, and fostering collaborative governance among public agencies, contractors, and financial institutions.