$400 for what? You buy the lift and they just slap it on or they supply everything and make sure everything lines up right?
I never priced installations, but body lifts are fairly easy. They are a bit time comsuming though. I took me about 8 hours doing most of it myself, including a little custom work to make everything line up properly.
I want to be a follower, but all the leaders seem to be lost.
I paid $700, total, for a 3" Trailmaster Body Lift with installation including custom rear bumper lift at Rocky Mountain Offroad Specialties in Grand Junction, Colorado when it was still open. They were the only ones who would put a body lift on my 1988 S-10, so your situation could be worse.