When it comes to billing, interior designers use many methods to calculate costs. Billing strategies vary, among other things, according to the size of the company and the scope of the project. Below are some of the most common methods interior designers use to calculate costs.Regardless of your pricing strategy, most interior designs cost between Rs 1,500 and Rs 12,000 for the designer alone, furniture costs not included. The average price for a typical house is around 5,000 rupees.