$35,200,000,000.00
30 ft tall 19 wide at the base 7 feet wide at the top, reinforced concrete on a 10 foot packed gravel footing.
Obviously no one here knows jack shit about poured in place concrete wall construction -- this is a 300+ year wall
A cheap reinforced concrete tilt up wall 30 ft tall with pile drivings and buttresses
$3,168,000,000 - $5 billion depending on the support.
I am assuming Davis–Bacon Act local prevailing wages.
Machine gun towers not included
Any earthquake repairs might get expensive.