At $100 / day for illegal labor, it's not a lot. Some of my friends hire illegals which I strongly disagree with, but they have no choice because their business depends on a flexible supply of labor. Regulations and taxes would kill the business if they hired legally. So at $100 / day, that's 8 days of untaxed wages sent to Mexico. That's not a lot.
Upon reaching this amount, money sent by fellow countrymen living abroad will become the main source of Mexicos foreign exchange, over and above revenue from crude oil exports that is expected to be slightly more than US$16.665 billion in 2004, and far more than income from visiting international tourists who will spend US$10 billion.
You'll forgive this Californian for not appreciating the benefit these folks bring to the economy.
There are agencies that provide day laborers. Because the laborer is employed by the agency, taxes and regulations apply to them, not the end user.
I have used laborers from agencies from time to time and been very satisfied with the cost and the work.