Definitely the tax payers of America are paying for this border wall and I don't know how Trump is able to state that Mexico has already paid for it using the new trade agreement and intertwine this two as one deal. I think it should be kept as two separate things.
It is like saying to the customer that since you have wasted petrol to come over to my shop, I would just give you a discount. I don't think it makes any sense. It's going to have some detrimental effects on the American economy and even the world economy on what Trump is doing. Maybe he just does something without thinking or giving some analysis but just do the things based on what he feels should be done.
I guess he should just name the wall as the Trump wall. Due to this tariff war Apple has lost its domination in China and it would in a way make Chinese companies much stronger. Why go for American products if it's gonna impose tariffs. I don't know how the trump won this election. I was rather surprised too as he hasn't any experience in politics but rather a better role for him would be just to run his business empire which he is good at doing for decades.
The initial payment for the wall will be from the US taxpayers. But the amount of money that the US taxpayer will save in the long run would be astronomical.
After the wall is built, all we have to do is raise the fees of Money Grams to Mexico. In essence, Mexico would end up paying for the wall in fees for money sent into Mexico from there citizens living in the US.