In addition to Fords $1,495 DDC my dealer adds a $395 doc fee and $130 title fee. Also a $499 winterization fee and $99 dealer branded mudflaps are typical up here but I politely declined those.
Kits are available for F-250s that convert the 4” to 8” for about $2000. Involves using FORScan to reprogram. I imagine there will be something similar provided as soon as parts are more available.
One side rail alone is $500, I don't doubt the $1,800 mentioned above.
https://www.tascaparts.com/oem-parts/ford-roof-luggage-carrier-side-rail-m2dz5455114aa?c=az0x