I think you could pay off the national debt. just by selling off the Presidio in downtown San Francisco right under the Golden Gate bridge.
But the GSA awarded a $435 million contract to design the new consolidated headquarters... and that is just for the design of the first phase.
And the GSA is a piker compared to unused buildings of the Post Office, Defense Department and other agencies.
Now consider the impact if the DHS had built its new consolidated headquarters in El Paso, TX or Niagara, NY rather than in the beltway.
The cost of government owned real estate location impacts government policy decisions related to their mission.