It depends on how well the kit fits, how much they have to paint (a lip kit like WW will be cheapier than a full kit like Kaminari), and if you want any custom work done. I would say the lowest for a lip kit would be $400-$500 and the lowest for a full kit would be $900-$1000.
I'd also suggest going to a body shop that you trust, since many shows will try to rip you off...
Lastly, please do a search next time, this question has been asked a ton of times. The search button is your friend and it won't bite so don't worry, just use it...