Senate Democrats: Cost for US-Mexico border wall could 'soar' to $70 billion U.S. Customs and Border Protection says estimates are 'premature.'

 -- Democrats on the Senate Homeland Security Committee estimated that the total cost of the construction of the border wall could "soar" to nearly $70 billion, according to a report prepared by minority side of the committee, which is led by Sen. Claire McCaskill, D-Missouri.

However, the report also says that "no reliable estimate of the cost of construction for the full border wall currently exists."

The findings were based on the per-mile cost was extrapolated from information provided by Department of Homeland Security to the Senate and then multiplied by the length of the potential border wall -- 1,827 miles.

The Democrats also looked at calculating the total wall costs based on cost estimates for wall prototypes proposals -- ranging from $200,000 to $500,000 for a 30-foot-long wall.

Based on those estimates, it would cost at least $64 billion to construct the wall, according to their report.

Those construction estimates don't include the potential costs of acquiring the land on which the wall will be built or maintenance costs, which may total nearly $150 million per year, according to the report.

According to U.S. Customs and Border Protection, any estimates of the "total border wall cost are premature as there are many variables that are currently unknown."

All historic dollar amounts noted in CBP's briefing on the Hill are associated with costs for legacy fence, acquisitions, U.S. Army Corps of Engineering expenses, etc. from the 2008 time period at specific locations, according to CBP.

"Costs cannot, and should not, be used to extrapolate future cost estimates for other locations," said a CBP spokesperson in a statement.

The budget request of $2.6 billion is to assist CBP with the implementation of President Trump's executive order, "includes significantly more than just border wall as technology and hiring are also key requirements under the Executive Order," the spokesperson added.

CBP said it cannot provide a more detailed estimate of the total cost of border barrier system until prototypes are completed and evaluated and design determinations are made.

The prototype construction is scheduled to begin on June 22 and finish by July 22, according to the CBP brief, which is in line with previous DHS statements that it would begin in the summer.

San Diego was chosen as the location to construct the prototypes because it allows CBP to compare to old barriers in the same area, the impact will be on "an existing enforcement zone" and land is federally owned, according to the CBP briefing provided to Hill staff.

There are currently 654 miles of fencing along the border and 1,300 miles with no border barrier, according to the CBP brief. There are 127 miles that are “unsuitable” for construction.

In the short term, DHS plans to use $20 million of "reprogrammed" funds to construct wall prototypes along the San Diego-Mexico border.

The administration is requesting $999 million in supplemental funds for fiscal year 2017 that would "continue real estate and environmental planning and design for high priority" areas in the Rio Grande Valley, Tucson and El Paso sectors.

If funded, DHS will construct 34 new miles of levee wall and border barrier system in the Rio Grande Valley, and replace 14 miles of fencing in the San Diego sector.

For FY 2018 CBP will request approximately $2.6 billion to construct approximately 71 miles of new border barrier in the same priority regions, according to the agency briefing.

ABC News' Benjamin Siegel contributed to this report.