The cost of a sauna can vary depending on the size, materials, heater type, ventilation, electrical work, insulation, benches, lighting, and whether you are building a new sauna or renovating an existing one. A simple refresh may only involve replacing benches, upgrading the heater, or improving the interior finish, while a full sauna renovation can include new walls, flooring, wiring, waterproofing, and custom design features. Understanding these cost factors before starting helps you plan a realistic budget, avoid surprises, and choose the right upgrades for your space and comfort goals.