Optical media are crazy expensive in Germany, especially the multi-layer ones. They are also getting harder and harder to come by, and horrible quality. Buy from Japan: they have a larger selection (though it’s also been getting less, recently), at lower prices (even after adding delivery and tax), and better quality. Try to get the ones made in Japan, the Indian stuff can also be sketchy (MAGBA*, VERBATIMf) though for some reason not as terrible as the crap being sold in Germany. Good choices in my experience are Panasonic for 25 and 50 GB (MEI.RA1, MEI.RB1) and the quad layer SONY.NQ1 (128 GB). They’re super easy to order from Amazon.co.jp, they’ll calculate the total price for you including anything payable at customs, so no bad awakening due to having to pay extra once it arrives. Not all JP sellers will ship to Germany, but most do.
I've done this for years now and can't recommend it enough.
Good luck!