It really does make a difference if you go to a more rural garage, rather than an inner city one.
I was quoted £180 by the same group, ie Arnold Clark, in Edinburgh itself. When I queried the Livingston dealer as to why they were so much cheaper, they said it was to do with the extortionate business rates in the city, which result in a far higher hourly rate.
So, if you know of any near you, outside the major cities, might be worth a small detour - certainly was for me
Gus