I can totally understand your concerns about this situation.
Let me tell you my story with the service cost of my Langematik Sax-O-Mat, maybe it helps to you:
I have sent my watch directly to Glashütte, the zero-reset mechanism doesn’t work anymore.
According the Lange service tarifs the service must be 1.400€ for my watch with a periodical, normal service and without polishing the case.
My watch was like new therefore I didn’t need a polishing.
I received the first sevice cost calculation ( Kostenvorschlag) with an amount of almost the double of the quote: 2.700€.
In this price the service department would have CHANGE some parts of the movement.
After I have asked it whether they can fix everything within a normal service they answered me that yes, they can REPAIR everything within the normal, periodical service, WITHOUT CHANGING the parts, only REPAIRING them.
I choosed this method and voilà: I paid 1.400€, I get back the watch in 4 Months, everything is perfect, I am happy!
So please ask DIRECTLY Glashütte - not via the Boutique - to REPAIR everything what is reparable and CHANGE only that parts what are UNREPARABLE!
You will get a new cost calculation with a much more affordable price calculation, I am sure!
And as you sajd: only Lange has the parts for their movements therefore I don’t reccomend to take the watch to an independent watchmaker….
I hope I could help to you!
Yours,
Adam