The people for whom €79 is not cheap are not getting flagship Samsungs, but some low tier $100-300 Android.

Here's a replacement battery for last year's S25 Ultra: https://www.mobilesentrix.ca/replacement-battery-compatible-.... Retails for 14 CAD or approx 9 EUR (11 EUR with a 20% VAT). So yes, 79 EUR would be extremely expensive.