I'm afraid I can't help you there, Elspeth. Wrong end of the country.
What I can help with, is maybe going some way to explaining why kitchen fitters are so reluctant.
Fitting worktops is a major part of installation. In some cases tantamount to a substantial rebuild.
With "new work", everything is known. One piece is fixed to the next etc etc. To remove and replace worktops, you have to know just how everything was fixed in the first place.
Yes, there are basic generic fixings and procedures, so for a good many of these jobs, everything is straightforward. That means a quote can be given, and stuck to.
What frightens fitters off is when non-standard improvisation is needed to just make everything fit. That of course sends any quote or estimate out of the window.
Perhaps your local Builders' Merchants know of someone, I'm sure they do. When you find one, you may have to be brave and ask only for a very rough estimate, then let him get on with it on an hourly basis.
I'm afraid it often comes down to trust.