Go to a scrappy and look for a 2.0 16V Ghia ..

Looking @ £20 a side, No more TBH ...

You will need:

1' Spindal - / - Hub - / - Caliper's.

2' Backing plate's.

3' Discs/Pads.

4' 2.0 - / - ST170 - / - RS Focus Rear Hose.

5' ST170 - / - 2.0 16V handbrake cable.

6' Maybe the ABS sensors if Applicable.

2.0 16v = 255mm Discs.

ST170 = 280 mm Discs.

RS focus = 280mm Discs, +8mm off-set.

Depending on front brake set up go for the 2.0 16v. (Cheaper)

I'de say £80 for the conversion depending on where you get the Handbrake cable, Discs and pads.