I guess the £4000 was to rebuild up to the original height. If that's not needed Lady A, then after removal, a decent brick/block layer could rebuild that stack very easily.
Ashlar blocks are available commercially all over the UK. There's nothing special about laying them except that the joints are very thin ...... approx 3mm.
I could point you to this page for info on indent repairs to ashlar. Indent only means cutting out the damaged ones and inserting new.......
http://www.historic-scotland.gov.uk/informguide-ashlar.pdf
For only a metre high, I don't think I'd even consider indenting. A re-build is so simple given a good access scaffold.
The leadwork has been bodged terribly as well. That would all be renewed at the same time.
I honestly think you should pull back and start again. Even from here, I hesitate to say it, but I do think both the £2000 and certainly the £4000 are greatly exaggerated.
It's a very simple, and not at all lengthy job. Perhaps you could look for a decent alternative builder.