Offer price to invoice price

Stay calm, Mr. Dx,

I am only inquiring about the legal status of things here and hope to receive a qualified statement.
It was never implied that I expected anything from a company.

PS: An offer binding period of 4 weeks does not by any means mean that the prices are no longer valid.

Best regards

A binding offer of 4 weeks does not at all mean that the prices no longer apply.

Double negation doesn't make it right.
A binding offer of 4 weeks means that the prices are valid for 4 weeks.
If you order after 16 weeks, you ask about the validity of the old offer and have it rewritten.
In my opinion, there's nothing you can do now except pay.
You could ask for a current price list (you will hardly get one), and compare it with the invoice.

Book under learning expenses, you can't do much more.

You are probably right that I have no other choice here. I would have wished for something else, but as WilderSueden already writes, it will probably be a lesson I have to pay here. Nevertheless, I just wanted to ask which legal bases apply here, or if anyone has had a similar case before and has a solution ready. In any case, thanks to everyone already. Best regards

(...) PS: Eine Angebotsbindung von 4 Wochen bedeutet noch lange nicht, dass die Preise nicht mehr gelten. (...)

Yes, that's exactly what it means. The offer is no longer valid. Also, any delivery date that might have been agreed upon would no longer have been valid. The verbal order you gave, without asking for a new offer, basically means "Do it, I'll pay the price you are asking." It's not that unusual. When I go to the car repair shop with the spare tire and need a new tire, I say "Please do it quickly"... I don't ask about the price there at all. And the master mechanic doesn't automatically tell me the price either. He assumes I'm aware that it will cost whatever it costs. Sorry, it always gets me a bit worked up because we have this debate with customers forever... some come back after 2 years and want the price we once guaranteed for 3 months...

Nevertheless, I just wanted to ask which legal grounds apply here

The legal basis is that you placed an oral order without an offer. So:

"Do it, I'll pay the price you ask"

A more interesting question would be what would have happened if you had placed a written order based on the specific expired offer 12345 and the craftsman had delivered without comment, without pointing out the additional costs. Then the craftsman might have accepted an old offer, although legally he could still have issued a higher invoice. But as interesting as that would be, it is not your situation.