What drives MERN stack development cost?

Five factors: (1) Scope: every additional core feature, integration, and user role adds engineering days. (2) Region: offshore India at $22 to $55/hr vs US at $100 to $200/hr for the same MERN work. (3) Engagement model: fixed-price adds 20 to 30% overhead vs dedicated team for evolving products. (4) MongoDB complexity: advanced aggregation pipelines, Atlas Search, and change streams take more engineering time than standard CRUD. (5) Real-time requirements: Socket.io, Redis pub/sub, and change stream architectures add $8,000 to $25,000.