Bt different for us, we had sash windows replaced. 14 of them. We ended up getting a builder (who was doing other work as well) to supply them. We specified the glass from Pilkinton, went to see a couple of joiners to look at the work. Very pleased with the result.
We originally looked at Everest. The price was £54,000, we laughed them out the door. They came back and gave us something like 40% off. We probed them about various details and they were lacking in info. I asked them about the British standards they claimed to have for wooden sash windows. They actually had none, they were for uPVC which made me more than a little cross. They sent round the local sales manager and he started to tell me how I could save money by not doing some of the building work so I could afford the windows. I showed him the door.
The building company came in at around £1000 per window, exactly to our spec.
It’s worth looking into smaller outfits and see if they can take you to see what you’ll be getting or get references of people they’ve done work for. A good job will last and will often be much more competitively priced. ALso look into what you are buying. We upped the spec on the glass from very basic to get a bit better energy efficiency and windows that looked nicer.