Well its really dependant what you want
Cheapest option I'd say is to go Plenum, Zorst, Utec, brakes and sus, I reckon you could do this for £5k probabley 20 hP more, but much better handling and brakes will make a hell of a difference
Second Option all in APS single turbo, which I think you can do for £5195 with WRC, thats all in on the road. I would always say do brakes and clutch, but not everyone agrees
Or You could Go Vortech S/C buy your parts from Performance Nissan in the USA, I Reckon 6 - 7 K all in for a good tune plus all additinal parts, maybe add brakes for another grand
Twin Turbo, you really need another couple of Grand at least and thats running without many elements that I would say are critical.