As I said, I had offers from 10 different construction companies in total, and for the windows, they were all between 4000 - 6000 EUR. That was too much for a bit of film, For 1800 I would have definitely done it. That’s fair.
Ask once if you can get the window frames foiled for 1800 and the exterior window sills in aluminum. We did it that way, saved 50%, and it’s hardly noticeable visually...