“Opinions vary” - snicker. Yeah, as to whether it would be $7 billion, or $10 billion, or $15 billion, or more. Tell me, do you really think - as impoverished as your intellect might be - that a single-strand barbed-wire fence strung along 6” diameter poles stuck in the ground every 3 to 4 feet is going to stop even the most effete of illegal immigrants?
No, I didn’t think so. That means that “cheap” is out of the question.
Truth is there are no valid estimate on what a fence would cost only scare tactics like yours. Get a life.
On the remote possibility that your figures "are even close" keep in mind the right fence will end or severely stop 100-150 billion dollars per year costs of illegals.
Such as 6.7 billion per year to jail them,welfare costs,terror threats-- how do you calculate another 911? What that will cost the nation,social costs,medical costs ever been to a ER room where the illegals flourish? You don't have a clue dude.