I need a hardware security key that would work with my iPad (Lightning) and my phone (USB-C).
https://www.yubico.com/de/product/yubikey-5-series/yubikey-5ci/ sounds like what you want.
With taxes and shipping, it will cost me 90 euros. Is there a way to get these keys cheaper?
Lukas did you search for a better price? Did the search turn up anything?