Here’s an enlightening article about the costs of incarceration and, incidentally, how much increased immigration detention has contributed to the coffers of the private companies that run prisons: “Prison Break.”
The increased emphasis on immigration enforcement means keeping more people detained, which is a costly endeavor, both in money and human costs, as illustrated on this page of the Detention Watch Network website.
And for those interested in learning more about the state of immigration detention – which is supposed to be merely detention, not punishment, because individuals are held while their status is determined, NOT because they are found guilty of any crime – here’s a report on the use of solitary confinement in immigration detention: Invisible-in-Isolation-Sep2012-detention. (See the Executive Summary for a quick overview of the findings.)
There’s lots more about this issue. These three sources are just an introduction.