We could just start annexing the provinces of Mexico and make them states!! Then they would have to pay taxes just like we do!
It is hard to wring money out of a rock and these places are dirt poor which is why the people are fleeing. We would be taking on a huge welfare burden and at a minimum all 100 million of those people would be collecting the Earned Income Tax Credit and food stamps just like they do in Puerto Rico.
West Germany tried this with East Germany and to-date the experment has been far from satisfactory.