Cost of fixed glazing with a reasonable U-value <0.7

Fixed glazing that cannot be opened

Yep, because you can "fall through". So safety glass or laminated safety glass.

Fall protection for fixed glazing that cannot be opened? Or did I misunderstand you?

Thanks
Daniel

Yes, to my knowledge, you will still need fall protection in the upper floor despite fixed glazing, to prevent break-through. Whether this is realized through a grille or break-through resistant glazing (TRAV) does not matter.

I think the window manufacturer or architect will insist on this for their own liability reasons.

At this size, with many giving up at 260cm, including shading, I would calculate 600 - 700 euros per sqm