The restoration of historical buildings is a complex and multidisciplinary process influenced by historical, technical, material, and economic factors. This paper introduces a novel hybrid methodology for cost estimation based on a decision tree structure combined with multi-criteria analysis, integrating both subjective (AHP) and objective (entropy) weighting methods. A unique contribution of this study is the development of the Intervention Effectiveness Index (IEI), which quantifies the trade-off between restoration value and cost. The inclusion of Environmental, Social, and Governance (ESG) criteria further enhances the sustainability dimension of the analysis. The proposed framework allows for the structured integration of expert knowledge, heritage guidelines, and cost-related parameters to optimize intervention strategies. A case study on historical masonry illustrates the practical application of this model, which is scalable to other architectural components. This comprehensive and adaptable decision-support tool contributes to more accurate, transparent, and sustainable restoration planning aligned with both conservation objectives and budgetary constraints.