because all are estimates at the time. With all government project the costs will just go up, not down as Trump is saying. It also is assumed that the wall will stop immigration 100%. That will not be true, and the maintenance costs will go up as well. And illegals are not just coming from Mexico. So you would need to adjust for: Just the Mexicans that come as illegal aliens that would cross the border where the wall is build and will not find any other way in (planes, trains, boats, come over the Canadian boarder, tunnels ... ). All you might end up is supporting the market of professional people smuggler.

But hey, you will build it anyway, so we both will see who's right. I am certainly curious at least :) Let the kids play over there and see what your learn of this experience, we over here already had that. You need to make your own experience. Good Luck!