Simons pretty much explained it. The system itself will cost the same whatever jets you run, but you can run it as a single hit system on 50 jets, exactly the same as I had at first, last year.
Its good fun but ultimately, gets to be a hassle having to watch the revs and not flick the switch until youre at 4 grand, plus youll end up wanting more power. Now Im running the 100s and progressive controller there is no way on earth I would go back to the single shot system. The full works is much safer for your car, you can use it even in 1st gear, off the lights or when youre already rolling. Basically its the system I had working when I easily kept up with the RB5 through Southend.
Depends how youre fixed for money but you could do what I did - get a basic single shot 50 hp system plumbed in, then later on rip out the wiring and hook up a controller. Ill help you out with the controller rewiring mate, as long as you dont mind getting the dash and scuttle panel off first, cos that is one job I hate.