For an ABS system you'll need the main loom, ABS modulator, abs front and rear wheel sensors, ABS front and rear wheel sensor rings, ABS relays, ABS instrument bulbs, ABS brake lines (flexi and metal) and splitter unit, R/H ABS switch gear for the 1150 or ABS reset/diagnostic button for the 1100.
And it would be beneficial to fit the higher rated alternator that's fitted to ABS bikes.
To fit the servo/abs you'll need far far more bits and pieces than the above, including the servo front and rear brake switches and different wheels

.
Not forgetting the labour involved, that is if you can find someone who'll be prepared to do the job.
I'd guess at an absolute minimum of £1200 to add ABS if you pick the parts up cheaply.