If you want to talk common sense... You can get the zex kit for $465 from
http://www.importcarpartsplus.com/ which is about as cheap as it gets. It'll also answer alot of questions people have about nitrous.
Nitrous will reach the cost of a turbo, but it'll take awhile a long while would be my guess. Assuming your just a casual, everyonce in awhile racer.
To clarify what I was saying: THE MOST HP FOR THE DOLLAR IS NITROUS. Also Nitrous WOULD come in handy in a race around a track.