In this lecture, we will explore the key components that determine the cost of an interior design project. The cost of various materials significantly impacts the budget, depending on quality, durability, and aesthetic appeal. Several factors affect interior cost calculation, including labor, design complexity, and location. By examining cost calculation examples, we can better understand budgeting for different projects. Lastly, we will discuss innovative approaches for low-cost interiors, which focus on smart material selection, efficient space planning, and cost-effective design solutions.