"That ... may be what finally gets us to actually close the prison. I mean the costs are astronomical, when you compare them to what it would cost to detain somebody in the United States," Gude said.
The cost argument could be a potent weapon at a time of running budget battles between Obama and the Republican-controlled House of Representatives, and of across-the-board federal spending cuts that kicked in in March. The "sequestration" as it is known, is due to cut some $109 billion in spending up to the end of September and has cut government services small and large.
Just one inmate from Guantanamo, for example, is equivalent to the cost of 12 weeks of White House tours for the public - a treasured tradition that the Secret Service says costs $74,000 a week and that has been axed under sequestration.
A single inmate is also the equivalent of keeping open the control tower at the Northwest Arkansas Regional Airport for 45 months. That control tower, another victim of cuts, costs $20,000 per month to run.
The $900,000 also matches the funding for nearly seven states to help serve home delivered meals to the elderly. Sequestration has cost Meals on Wheels a median shortfall of $129,497 per state, the organization says.
Or measured in terms of military spending and national security, the cost of four inmates represents the cost of training an Air Force fighter pilot - based on the Department of Defense's figure of $3.6 million per pilot.