The energy cost of sea transport is like 50 less per distance traveled than on land and it has being like that for the last 3000 years. So the cost of shipment to Netherlands is just a cost of transporting to the nearest sea port from Sahara.

Iron is heavy, dense as a material, but the cost-efficient of moving it around as an energy store depends on it's energy density (and it's initial cost), not it's basic density as a material.

you need to run your ship on iron fuel as well. I guess that is the test though, can it ship itself?