it might be cheaper to fit the nos kit.....but by the time uv paid for the kit...and had a play, and emptied the bottle a few times...with each refill, the price comes closer to the cost of permanent power upgrade to ur car.
personally....id use nos only when i have the engine tuned to the max, and its nigh on impossible to get more out of it..
nos imo , is the last ditch attempt to get the very last out of an already heavily modified engine.....