I know there’s going to be lots of variation in this answer, so I’m going to define my terms.
City: Springfield, Illinois. A city of 110,000 in the Midwest US.
Home: A 1,400-square foot ranch. Prototypical lower-middle-to-middle-middle-class house.
Rooms: Living room, kitchen and master bedroom.
Ideas: Nothing too exquisite or over-the-top. I want my rooms to look more appealing than the haphazard mishmash of (pre-makeover) decorations that typifies what I see on design shows like Trading Spaces, but I also want design in keeping with my somewhat humble surroundings. Furniture from Sears; that kind of thing.
So, yeah. What do designers typically charge? Do they buy all the furniture, hire the painters, and send you one bill? Do they charge by the square foot? Anything else I should know?