A 10% surcharge on money flowing back by wire to Mexico would be a good start.
Hell, simply using the money we give them “officially” works. Why have foreign support for a country that deliberately promotes our invasion?
I think the 971 nillion in foreign aid we give to Mexico would be a good start in expenses to build the wall.
10%? How about just enforcing the current laws on the books which takes all of illegal alien ill gotten gains then fines those that gave it to them?