Mexico may also pay some of the bill, but the USA will undoubtedly pay more (I'm guessing 80-20%). And building the wall is unethical from the USA perspective... In 2015, when Hungary built a fence/wall on the Hungarian-Serbian border (to prevent the influx of migrants into Hungary), it was the USA that sharply criticized this, saying that it violated human rights... Of course, we know...there are always those who are "more equal" than others ;)