In resource-constrained higher education institutions (HEIs) and Open and Distance Learning (ODL) systems across developing regions and emerging economies, escalating commercial textbook prices and recurring digital software licensing fees impose severe structural barriers on student access, persistence, and institutional fiscal stability. Open Educational Resources (OER) have emerged as a transformative operational and economic intervention, enabling institutions to replace costly commercial acquisitions with collaborative, openly licensed learning assets. Grounded in the CIMO (Context, Intervention, Mechanism, Outcome) framework, this systematic literature review synthesizes empirical evidence on the economic sustainability models, cost structures, and operational outcomes of OER adoption published between January 1, 2000, and December 31, 2025. Comprehensive searches were conducted across five electronic databases—Scopus, Web of Science Core Collection, EBSCOhost, ProQuest, and JSTOR. Following a rigorous two-stage screening protocol and critical quality appraisal using the Mixed Methods Appraisal Tool (MMAT) 2018, 36 empirical studies meeting all eligibility criteria were included in the synthesis. The synthesized findings reveal four primary economic mechanisms underpinning sustainable OER ecosystems: (1) capital reallocation from proprietary commercial licensing to internal open content adaptation and localization, which yields 65% to 92.6% direct per-course cost savings for students; (2) inter-institutional labor sharing, cross-campus consortia, and librarian-led communities of practice, which reduce duplicative curriculum authoring labor by 34% to 45%; (3) shared digital repository infrastructures and standardized API architectures, explaining 36.4% of the variance in institutional curricular adaptation agility and reducing emergency transition costs by 48%; and (4) the microeconomic amortization of course creation fixed costs across large distance learning cohorts, generating 22.4% to 35.2% reductions in per-student institutional unit delivery costs while lowering course dropout probability by 22%. Although the evidence base exhibits minor methodological limitations related to self-reported survey data and geographic imbalances, the overall body of evidence demonstrates high certainty under GRADE and GRADE-CERQual frameworks. Ultimately, OER facilitates a strategic transition from recurring commercial procurement to capital-efficient collaborative commons production. To guide future scholarship and institutional policy, an integrated Input-Process-Output (IPO) conceptual framework is formulated alongside six testable research propositions.