According to listosaur.com, Mexico received $757.7 million in aid from the United States in fy 2011. The total aid is currently lower, following cuts due to Mexican human rights violations, and the arrest of a US Marine who unintentionally entered the country with firearms.
But even so, there is still a more than sufficient annual sum to cover the cost of a border wall between our country and Mexico. So in effect, Mexico can certainly be made to pay for the wall, all Mexican avowals to the contrary notwithstanding.
The Unveiled Feminist 