If illegal aliens were given amnesty and began to pay taxes and use services like households headed by legal immigrants with the same education levels, the estimated annual net fiscal deficit would increase from $2,700 per household to nearly $7,700, for a total net cost of $29 billion.
Costs increase dramatically because unskilled immigrants with legal status -- what most illegal aliens would become -- can access government programs, but still tend to make very modest tax payments.
Although legalization would increase average tax payments by 77 percent, average costs would rise by 118 percent.
The source
Center for Immigration Studies