But wait don’t you have to know what materials are called for in what quantities and made to which specification before you can estimate the costs?
$2m per mile is more like a generic wall of indeterminate height and structure.
Is this wall free standing? Does it go beneath the ground and if so how far what is the height above ground? are there another features such as pointed spikes, razor wire an the like? How many sensors and of what mix are included? how are they placed? how do they send their data? how is that data used and interpreted? What’s the cost of building the data center? ETC
All of these add to or subtract from the cost per mile. What are the difference and what are the similarities to the Saudi and the Yemeni walls?
Similarities: multiple layers of barbed wire with on the ground barriers, ditches that prevent someone driving a truck through, guard posts at regular intervals, lights, communication networks.