Stupid question but when they ripped out the old one to put in the new one I'm assuming there's making good to be done. Is it typically some plastering and decorating inside or is it on the outside?
They patched and sealed everything. Probably depends what they are replacing but they didn't make much of a mess outside the boundary of the windows they were installing. And some of the trim covered up the plaster/wall edges.
We got Everest uPVC sash windows, all about 6' tall and 3' wide, came in around £1k per window.