You can expect to pay anywhere from $150 to $500 per hour for a design plan and full implementation of the interior designer charges an hourly rate.however we prefer to charge based on the square footage of a room, with a minimum of $300 per room. The fee includes a design plan, shopping list and design board. we also offer a discount for three or more rooms as well as shopping assistance for an additional $75 an hour. The costs associated with hiring an interior designer will vary quite dramatically from job to job. One homeowner may ask for help with their entire home, while another wants some professional assistance in the family room. The smartest approach is to meet with a few designers, take a look at their portfolios, discuss the project you need assistance with and hear what their thoughts are on the work. You can then request a bid for the work, and wait until you have three candidates from which to choose.