> Bare-metal on Hetzner now has a setup fee of up to 350 EUR.. you can find some stuff with 0 setup fee, but it's usually quite old kit.

I don't understand what you are paying for here, nested virtualization doesn't need any extra setup for hardware compared to normal one

... or you are saying Hetzner wants 350 EUR for turning on normal virtualization option in BIOS ?

Hetzner charges a fee for setting up your bare-metal machine. Often zero for their smaller machines and for those in auction. Probably they don't want someone to order a large fleet large of machines for one month and then cancel. They might not get another customer for those machines soon.