40 billion USD is maybe Trump change but not chump change. That wall will take years to build too. IIlegal immigrants from Mexico add more to the economy than they cost. In any case, the panic about illegal immigration is overblown. A lot of the panic and rhetoric can be traced back to an article by David Frum, a speech writer for Bush, currently sucking dick as a freelance writer to serve right wing causes. Facts are difficult for you but I'm going to lay this statement on you just to irritate:
"Legal immigration has always been much higher than the illegal kind, and illegal immigration is now close to zero. But Frum’s main argument is about legal immigration, and he effectively claims that some groups of immigrants are undesirable."
http://www.bloombergview.com/articles/2015-12-23/low-skilled-immigrants-don-t-drag-down-the-u-s-
The issue regarding that wall is all about racist attitudes and nothing else.