Securing sustainable capital mobilization and structuring viable long-term financing mechanisms represent pivotal challenges for advancing Renewable Energy Auctions and Regional Grid Integration throughout developing Asia-Pacific economies. This research develops an integrated financial-economic framework evaluating domestic resource mobilization strategies, thematic debt instruments, blended finance facilities, and private capital de-risking mechanisms. Utilizing multi-country capital expenditure datasets and multivariate econometric regressions, the paper quantifies investment elasticity and sovereign risk premia across varying macroeconomic regimes. The empirical results demonstrate that implementing standardized taxonomy frameworks, credit guarantee structures, and local currency bond market instruments can reduce sovereign borrowing costs by up to forty-two basis points while unlocking substantial institutional capital flows. Furthermore, the analysis identifies crucial policy prerequisites, including green budgeting reforms, fiscal risk buffers, and transparent disclosure protocols essential for preventing fiscal stress and debt unsustainability. The study concludes with practical recommendations for fiscal authorities and multilateral development institutions to establish interoperable sustainable finance platforms, catalyze private sector investment, and bridge regional financing gaps.