I'd take the 80 Euro and also ask for a credit line and a couple dozen calendars for you to have for your portfolio.
You're not bargaining from a position of strength. They'd like to use your picture, but if you demand too much, they can certainly find another image to use. I say that because, if they publish the calendar every year, they no doubt have regular contributors and sources for pictures.
Having the picture published and being able to show it around, even if it is only to show your kids and grandkids, will be worth much more than the 80 Euros, which will soon be gone.
+1 I'd run with that. Be glad they've chosen to offer you compensation for one of your images, enjoy the "props" that go with it and get a dozen calendars to share with some of your family and yes, do make sure you get a credit line...
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