I just had one done for my MOT.
It depends really, I got the part for £57 genuine, so bargain as well.
However it can take up to 2 hours labour to do it, depends how seized the bolt is that holts it in, they can be a pain to get off, it varies, luckily it came straight off on mine apparently but on some Punto's it doesn't because the inner sheath rusts to the bolt and you can't get to it, so you have to heat it up and keep using some force to get it off.
I'd say no more than £100 for the job including parts.