In 2017, $31 billion was sent to Mexico by Mexican expats. (That's total, not broken out for US.)
http://www.worldbank.org/en/news/press-release/2018/04/23/record-high-remittances-to-low-and-middle-income-countries-in-2017
Mexico's GDP for 2017 was approx. $1.1 trillion.
https://countryeconomy.com/gdp/mexico?year=2017
Not a mathfag or econfag, but it sure looks like a substantial part of Mexico's economy is based on remittances.