You could run it stock and keep it very low boost. Same with a decomp plate but all the other bits will cost good money.

One budget zetec turbo route is the st170 / Zetec hybrid.
st170 bottom end with a set of Arp rod bolts.
Your 2.0 Blacktop top end with the st170 valve springs.
A thick head gasket.
You may as well give it a refresh with oil seals, valve stem seals and bearings.
Cr around 9:1

if your counting both base engines this is an easy grand.

Another option if your engine is good.
Focus Rs pistons.
Forged Rods
Valve springs.
full refresh.
Cr around 8:1

A good £1500

you will need a turbo, Td04 are cheap and reliable but will be maxed out at around 275bhp.
Injectors at this level will be 440cc~660cc range.

gearbox, you will be looking at an mtx75 conversion.
A descent 240mm clutch, something like the Focus Rs.

Intercoolers, plumbing.

I've found the hard way the list really does go on and on.