I could be wrong, but didn't Trump do an end run around congress by having the military build it? Army corp of engineers?

My guess is that Mexico will be paying for it with the tariffs being collected. .

If Biden stays in office for more than a few months, the money to build the border wall will come from Mexico.

THEY will build that wall higher to keep Americans from crossing and fleeing our own economy. :>)

I recall the money came from the Pentagon after Trump cut the wasteful Neo-con and prior Hussein Admin spending. It seems this action by President Trump ended up in front of SCOTUS. They ruled in his favor, but not unanimously.