Construction fag here.
POTUS has done the most efficient thing possible for the wall.
He's modularized it.
The first $1.6 billion could have gone to every medium to large fabricator along the route.
These sections are simple.
Straight tubes, flat welds, no sandblasting, no paint.
The Rebar for footings is prebent and simple to install.
The sections look to be about 6 feet wide which means that you can build them anywhere and transport them on a standard truck.
No wide loads or escorts.
Standard 5000# plant mix is more than adequate for this task
No need for portable concrete plants.
Just source it along the way
Essentially, dig a ditch
Set the section
Weld or bolt the top
Set the rebar
Fill the hole with concrete
Pull out the temporary bracing.
A ten man crew with 3-4 pieces of equipment could put up a half mile a day without too much difficulty.
He's had two years.
There could be thousands and thousands of prefab sections ready for install