what raj has said is true, could be done for less though.
however there are a few things to consider really, management is one, i'm using megasquirt 2 and that will set you back around £350+a laptop, wideband and loom, so nearer to £650-700 then, but no costs in tuning from then on.
then there is injector to consider, some 630cc siemens dekas will see big potential and not so expensive from the states (mine were about £200 including customs charges )
turbo is something to consider too, either a 4wd cossie t3 or a T34 would instantly spring to mind unless you can get hold of a GT30 cheap enough.
forged pistons and H section rods are a must in my opinion, anywhere from £800-1000, but well worth it in the long run.
inlet could be an ali zetec one, or a custom made plenum wouldn't be that expensive circa £300.
you could tap the zetec head for an ERST manifold to save some cash or a tubular could be made from £250+
uprated valve springs are a must for anything over psi of boost and standard cams will be plenty good enough for 300bhp+

i have a 1.8 zvh and that's using early skimmed pistons, although rings have started to go now and i'm planning my 2.0 forged full zetec.

a zvh is good enough, but it has a big torque surge and will wreck an ERST box easily on 23psi of boost lol!
zetec is much smoother in power delivery and has more tuning potential, i've heard of 400bhp zvh's, but 522bhp+ zetec turbo's, plus they're better on fuel and you can tinker with valve timing to benefit you more too.