If you want to build a wall, then not only do you have to build it, you have to maintain it and you have to have stations all along it, ask the Romans and Chinese about walls, if you want living memories ask the Germans. Then look at the governments that built those walls.
Once you have built the wall you then have to patrol the seas and bury the bodies you fish out, ask the Italians about that one. Ask the French and the British just how hard it is to prevent chaos at the border crossings and that is without mass deportations.
Now if you want to send all the illegal immigrants home during your terms in office, that is roughly 5,000 per day, every day, for 8 years. Think of the logistics, the personnel requirements, ask the Nazis about just how much infrastructure that entailed. Then what do you do with them. What do you do if the countries where you want to send them say, no thank you, declare war?
On foreign policy, it gets no better, first we piss off our allies in the region by refusing to deal with them unless they fork out the cash. Then we launch ground wars, again. Now we have to start expanding the military to make up for our loss in allies willing to join in. Just how large does our Imperial army have to become?
So we now have an Imperial Army and whole army employed to deportation and immigration control. How many new government employees do we need. Don't forget the logistics and internment camp infrastructure and personnel. This will dwarf any savings made by closing the rest of the government down so that business can prosper. Of course the extra cost will be covered by cutting taxes and blackmailing the rest of the world to pay for it all.
From what I gather however, all this will be carried out by means of Trump's personality and a magic wand.
I suppose the hope is that if Trump is elected, that Canada and Mexico will pay for the border control themselves, in trying to keep Americans out.
Be wary of Authoritarians in Government, since they tend to love just organizing and controlling your whole life. If you work in a global corporation, you know just how that works. Object? You're fired.