According to this story, the awful and expensive wall is likely to cost well over 15 billion. If Trump has any involvement in supplying companies it will probably be many times 15. Here's the latest.
Tony, I think it will cost more than double that amount. The main reason is the "terrain" and getting workers who want to work there and stay in trailers at the job site. Also getting all the equipment there as well building materials. Especially don't forget "protection" day and night. Furthermore as soon as one piece is built the "ready piece" will attacked or damaged from the Mexican side or tunneled under. Then "the weather" the river will go beyond its banks and undermine the "wall"
Logistics will be an disaster anyway you look at it. Just one big question: Have you ever seen an Government project which was on "budget" and in "time"??
Another funny thing which makes this "wall" obsolete is that they found an huge catapult on the Mexican side of the border with which they launched kilo's of drugs into the US. Furthermore they are also using drones now to drop the merchandise. Thus don't worry no shortage of "weed" or the stronger stuff in the near future.
I guess if Trump keeps spending millions on his outings to his "palaces" then there won't be any money left for the "wall"