The size and scale of your trim project will help determine the time and materials that are needed for the job. Average prices for installing trim in the U.S. range from $318 for a 100-200 square foot area, $387 for 200-300 square feet, $543 for 300-400 square feet and $617 for a 400-500 square foot space. Crown molding adds a dramatic trim feature to any room and is available in countless profiles to suit your design scheme.