If you got the time and a few basic tools, you'll save quite a bit if you do it yourself.
Most decent lumber/ hardware stores will help you out with a material list. Get a good idea of what you want (Drywall, paneling- whatever) and your measurments- Length, Height and width of the wall.
What kind of stuff do you want on the wall? Outlets, cable, speaker wires, etc.... Right now is the time to put that stuff in.
And if your wife is anything like mine- send her out of state for the weekend. Nothing kills my confidence like having my wife stand right there gasping whilst I fasten a wall to the floor and ceiling.
If you go the contractor route- Ask down at the lumber yard. They tend to have the inside scoop on who is reputable and does decent work.