For anyone wondering it is $70, meaning £67 or €69 (DE).
Where did you find that price? On the official purchase page[1] the lowest price is 97 EUR (which is around $113)
[1] https://www.raspberrypi.org/products/raspberry-pi-400/?resel...
I did a double take as well, and had to look it up.
However, there's a simpler reason: for psychological reasons no retailer is going to voluntarily put higher prices on their shelves than they have to, and since unlike most other countries there is no consumer protection law requiring the the actual checkout price including sales tax to be displayed, they don't.