Ford charge £58.56 for the part but third-party replacements are available online for around a tenner.
Adding in the labour and the VAT, £57 seems like a very reasonable price to me.
My own local mechanic, who does an excellent job and who is far cheaper than main dealers, would probably charge me £35 + VAT = £42 for labour if I provided the part myself.
A Ford main dealer would probably charge at least £120 in total (if not far more), so you're getting it done for no more than half price.