^what they said. It won't be cheap, my buddy has a narrowed 9" in his 350 s10 with Moser axles and whatever bolt pattern is on a stock s-10 (i forgot, I think 5x4.75) I believe it ran him $1,500. His is lincoln locked i think... (again can't remember) and the thing gets stupid sideways with a turbo350 tranny and a claimed 400hp (pry more like 300,320), I can only imagine how worse it would be if he ever gets a 5spd swapped in. Oh and he's got... shoot I think like 3.88's.
I don't know if any of that is helpful (or if it even had a point) but in my own experience, it doesn't take much to get a truck sideways as long as you know how to use a stick.
Whatever you do, build it right and don't take shortcuts. Cage, tuned suspension, axle and engine swap. Oh, and keep it on the track not the street.