According to CNN MONEY in September, 2016:
Almost $25 billion flowed last year  from the pockets of Mexicans living overseas, almost all of it from the U.S. That’s even higher than what Mexico earns from its oil exports.
The average remittance in June was $300.08, which when multiplied by the number of Mexican workers abroad totals billions each year. Donald Trump has his eye on those billions — earlier this year, he said the cash could pay for the wall he has proposed between the U.S.-Mexico border, even though he didn’t mention that in his meeting with Mexican President Enrique Peña Nieto on Wednesday.
Essentially, Mexico’s most lucrative natural resources are the people who leave home. The cash remittances are a lifeline for the country and a critical source of economic development for America’s southern neighbor.
Now, the figures for 2016, From Pew Research.
Worldwide, an estimated $574 billion (USD) was sent by migrants to relatives in their home countries in 2016, a 1% decline from 2015, when the amount was $581 billion, according to economists at the World Bank. This is the second drop in global remittances since the global financial crisis. Despite this recent decline, remittances sent by migrants are still about double what they were a decade ago, before the sharp decline in the global economy during the late 2000s.
Tracking remittances worldwide is difficult because many countries do not track funds that are sent or received. Based on data it is able to collect, the World Bank has used a statistical model to estimate the amount of money coming from each sending country to each receiving country. Because these numbers are estimates, there is some room for error. For example, the total incoming or outgoing remittances for some countries may not be the same as actual remittances.
I’ll bet that a tiny tax on all of those dollars being sent out of our country would more than pay for The Wall. Considering that much of the money is under the table and, therefore, untaxed, it only seems fair. If the tax was applied to all foreign remittances, it would probably cover the cost of border patrol and ICE too, and even some of what HSS is spending for housing illegal aliens. The Unaccompanied Alien Children Program costs almost a billion dollars this year alone.