A gallon of paint costs $15 to $40 and covers about 350 square feet with one coat. Designer varieties can run over $100 per gallon. Your contractor pays 50 percent less than what it runs in a home improvement store. You’ll also need to spend another $20 to $100 on supplies like brushes, rollers, masking paper and plastic. A professional will have these items on-hand. Westminster House Painting CO