It's not easy to quantify the cost of illegal immigration. For every kid who goes to school or gets medical treatment on the taxpayer's dime, there are ten families worth of illegal immigrants who pick our fruits and vegetables, bus our tables and take care of our yards at a rate significantly less than minimum wage. So whatever you put into the collective American pot that goes toward taking care of the cost of illegal immigration, you probably get back in services and goods that cost much, much less than they would if it were American citizens holding those jobs.
So there are mix of variables when trying to determine the cost of illegal immigration. And what makes it an even harder topic to tackle is that the topic is a political hot-button issue, with republicans and democrats lined up on opposite sides of the aisle ready to leap to attack (or defend) depending upon what you say, think or do. In the process, facts have become less of a concern than maintaining lockstep dogma with those on "the same side as you."
Some things to understand when figuring out the cost of illegal immigration: The United States government does not spend 11 to 22 billion dollars per year on illegal immigrant welfare. This is a popular canard trotted out by the Lou Dobbs'es of the world, and it's not based in fact.
That's actually a good rule of thumb: If the information you're getting on the cost of illegal immigration comes from Lou Dobbs, or comes from a report that links to Lou Dobbs, or comes from someone who watches Lou Dobbs on television, it's a compromised source. Dobbs's personal income is based upon maintaining viewership for his television show. When viewership started declining, he began to use harsher and harsher rhetoric toward illegal immigrant. This caused viewership to go up. So he got even harsher. And got more viewers.
So in essence, Dobbs fabricates information about the cost of illegal immigration - usually going out of his way to make them as outlandish as possible - for money. If someone's doing something so egregiously for cash, you have to take their "facts" with a grain of salt.
For example, Dobbs once said that a full thirty percent of prisoners in American jails are illegal immigrants. This is patently false; a CIS report put the number closer to eleven percent. While that's still a significant percentage, that doesn't change the fact that Lou Dobbs is a liar.