Amnesty quid pro quo
If 10 million of the undocumented immigrants living in the U.S. each paid a modest $2,000 for an "amnesty ticket," the $20 billion would pay for the next 1,000 miles of wall. Then, with the border substantially secure, we could implement a controlled immigration flow. And ticket holders could live without the fear of deportation as long as they abide by our laws. Everybody wins.