I think its £40 but they are pretty simple to install.
Just get a set of stereo pins for about £2, pop em in, take out the headunit, pull out the wires, put the new ones in, tuck them at the back.
Put the new headunit case in, use a screwdriver to push the pins in so its stays, connect it up and good to go.
The new one will have instructions which are pretty easy to follow if you need them