I suppose if you got a T38, 750cc injectors, mapped, plus other incidentals (boost hoses/air filter/cam(s)/coil pack/whatever) minus what you could sell on from the previous build, you could be up and running 440ish brake for around £1500.

If you decided you wanted an internally-gated, or even exteral, GT30, then your wallet better be a lot bigger (pistons, head work,cams,etc)

Your best bet is to decide what your budget is and talk to your tuner.