BOM estimates don't indicate X60 is any more expensive. As Qualcomm's first 5nm 5G baseband, it's probably necessary in this case for power efficiency.
The new iPhone SE is not compatible yet with some Italian 5G providers, like Iliad, whereas iPhone 12 and iPhone 13 do connect to their 5G network. It seems it is something related to the fact that N78 band on the SE is 2x2 mimo and not 4x4, which is the 5G standard, therefore it needs to be certified to operate on the network. Tested on ground.