Ironically, the money sent to Mexico doesn't really hurt us. What can a Mexican do with American money? Spend it. On what? American goods. After all, the money is no good in Mexico. So the payments sent to Mexico actually benefit our export industries. The money comes home.
There are enough real problems with the flood of Mexican illegals that we don't need to confuse the issue with a non-problem.
The real benefit from putting a cap on the amount sent to Mexico, or a tax on the amount, is that it makes it no longer profitable for the Mexican government to encourage emigration and remittances. Is that worth the trouble of enforcing a tax or a cap? I'm not sure. I think there are more effective things we can do.
Actually the best answer economically is to do nothing and let the market forces determine the number. Once there is full employment among the Mexicans the excess will move back home. As long as there is work they will come.
Pray for W and Our Troops
As long as there are not similar "penalties" for sending money to countries beside Mexico, no one is going to be stopped from sending money to Mexico through one of those other countries. Next solution?