Dwarves on the Border!
Not a "little" harder.
It will be MUCH harder. Those walls were probably a mixture of a few tens of feet of outdoor set and computer-generated imagery.
A real wall of that size would consist of 2,100 miles of concrete and rebar stretching tens of feet skyward.
It would thus be much more expensive.
Did you see the movie, yet? Did you get a load of all of that potential advertising space?
I haven't seen the movie. I've read the book, and I know what you're talking about.
Why we can pay for the construction of the walls, their maintenance and upkeep and retire the 'national debt'!
Advertising costs depends in part on how much traffic goes past the point where the advertisment is placed. On most of the US-Mexican border, that traffic, excluding jackrabbits, coyotes, and rattlesnakes (all of which do not have money), is "nil," which in turn indicates that the advertising revenues will be nil. You wouldn't even break even on the cost of building the walls.
A construction plan from 1978-1981--the MX ICBM Mobile Protected Shelter (MPS) basing concept in the Nevada/Utah Great Basin--would have been the largest public works program in the history of the United States had it gone forward. It was killed mostly due to the enormous price tag it would have cost if everything had gone perfectly. The missiles wound up getting built and stuck into existing silos in Wyoming, so they weren't the main issue.
Your proposal dwarfs the MX MPS program by a wide margin, and would probably not survive Congressional debate as a result.
Dwarves on the Border!
Ah, but you didn't say we wouldn't make any money at all. So, how much do you believe we would make?
Would the advertising cover half the cost?
What was the projected cost of the MX ICBM project back in 1978 - '81?
With the walls providing protection and security, more people might be motivated to live near the border.