I read it was about that amount, too. And, the remittances are the #1 revenue in Mexico.
I saw a news report or documentary several years ago that showed a school buses coming over the border every day, dropping the kids at California schools, then picking them up and taking them back across the border to Mexico in the afternoon - that’s insanity!
Read an article this past week that not as many are coming in from Mexico now, but rather from Central America.
One other thing that needs to be stopped immediately is all the planes of Chinese pregnant women being flown in (at a rather large expense to them), staying in the US (primarily CA IIRC) then flying back home - presto, baby has dual citizenship. As you said, we need to end anchor babies, but this practice by the Chinese (as well as Mexicans and others), needs to be stopped immediately.
Sounds like a "baby visa."