Interior Designers might seem like their services are too expensive for what you are getting in return, but consider this, before dismissing an interior designers worth:
How much time would it take for you to measure your entire home? (Including the baseboards, window sill and trim, doors, door frames, distances from electrical outlets, switches, counter-top height, width, depth, floor length and width, stair riser height, etc.) Designers are pro's and they can do this in a matter or a couple hours or less depending on your home and designer's skill.
How many phone calls are you willing to take during your work hour(s) or after from contractors, vendors, delivery personnel, etc? Do you know what to do if one of these people doesn't show up? Do you have someone else you can call to fill in for someone who may call out sick that day? Do you have someone who will be home when you are unable to be there to accept deliveries? Designers have all the resources they need, including people to receive packages when you can't be home. We all have busy lives, and adding one more responsibility to your plate might be a little too much.
How much time do you have to track all your packages and follow up with vendors who don't follow through on their delivery dates? Designers often spend a good portion of their day tracking purchases for their clients, making sure all deliveries are on time, and if they are not, Designer's will handle the situation, often behind the scenes, so you don't even know what they are doing- creating more free time for you.
Not only do designers do everything listed above, but they also have an education that helps them select the best materials for your home given your personal criteria. Got pets? No problem, designers can pick materials that will with-stand claws and paws. Got kids? No problem, designers will find stain resistant fabrics for you. Got antiques or family heirlooms? No problem, designers know what kind of window treatments you will need to keep them save and damage free (at least from the natural elements).
This is why everyone needs a designer. Even if only for a few hours, be sure to make friends with your designer so you have someone to call in case you need some help! Don't be afraid, they wont bite you!