"DHS plans to spend billions of dollars developing and deploying new barriers along the southwest border. However, by proceeding without key information on cost, acquisition baselines, and the contributions of previous barrier and technology deployments, DHS faces an increased risk that the Border Wall System Program will cost more than projected, take longer than planned, or not fully perform as expected," the GAO said.
Homeland Security border wall prototypes fail to account for rough terrain →
The Government Accountability Office said costs can vary considerably based on the slope and topography, land acquisition costs and other factors.