It will cost, according the candidate, somewhere around US$3 to 10 billion. That much should buy a really nice wall.
Of course, he wants Mexico to pay for our wall. Nifty.
Since Mexico will not voluntarily pay, and why would anyone, Trump will have to coerce Mexico. His plan is to stop money transfers into Mexico. This is US$25 billion a year into Mexico's economy. This will anger Mexico.
Still, on the face of it, not a bad deal. Mexico sends a one time transfer, and they get to keep all the money they from the US. This does not include the US$135 million in foreign aid to Mexico.
Trump intends to do this through the USA PATRIOT act. It is dubious legally. To say the least. Probably ineffective, as well. I example, say I want a Monte Cristo #2 Habana ("Habana" is the correct term for a Cuban cigar). I call my friend Julio at J & J Habanas in Cabo. He Fed Exs the cigars to Tijuana. They are walked across the border, then Fed Exd to me. Something like that would happen. No law will stop someone from helping the family. Or wants a cigar.
Certainly, build the wall. Until we control immigration, we cannot reform it, and that is necessary. Do not dither with Mexico, trying to get them to pay. It is a waste of everybody's time. Obviously, attractive, single females who wish to immigrate should be handed a passport at the border. Clearly, as the Hot Chick Exception applies to women in prison who had committed some slight sin like murder, it can be applied here.
Also, talented soccer players should be allowed in, as long as they decide to play for the good guys. If he then decides to play for El Tri, deport him the next second. With a kick in the ass, but only after the penalty for treason is explained.