Illegal immigrants are a net loss to the U.S. Taxpayers of $27 to $72 billion dollars annually depending who you ask and the various factors they use to make their calculations.
According to the C.I.S. an illegal immigrant will be a net average loss of $55,000 dollars over their lifetime and the Libertarian, CATO institute pegs it at around $89,000, I believe.
The government's not able to hide anything, really. The federal government's portion of the 'National Debt' is over $6 trillion dollars and add another $28 trillion for the rest of the total debt we're in as a Nation.