Every single illegal captured in the US should cost the Mexican government $10k or so. Which would go to fund the wall, and pay for the employees which will all be illegal immigrants. Paying off their debt to the US public.
$10k* x 50 million illegals = 500 billion dollars. We can build the wall out of platinum.
(*Frankly, it ought to be higher than $10k per, it should be between $100k to $1 million depending upon the damage and cost said illegal has inflicted, perhaps higher)