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Story highlights

There's no exact figure for the cost of President Donald Trump's border wall

Republican lawmakers have pushed back on funding the project

(CNN) —  

President Donald Trump vowed Saturday to keep costs down on his proposed wall along the US border with Mexico, although he did not specify how much one of his signature campaign promises would cost.

“I am reading that the great border WALL will cost more than the government originally thought, but I have not gotten involved in … the design or negotiations yet,” Trump wrote in a series of two consecutive tweets. “When I do, just like with the F-35 FighterJet or the Air Force One Program, price will come WAY DOWN!”

The President has not yet released a specific plan for the wall, including an exact cost, though on the campaign trail Trump has cited a $10 billion estimate from the National Precast Concrete Association. But other outside estimates suggest there are enough variables to cost up to $15 billion, and possibly as much as $25 billion, according to a report from Bernstein Research.

RELATED: Here’s how much Trump’s border wall will cost

The President campaigned on building a wall along its Southern border to stop illegal immigration, and even before occupying the White House, Trump’s transition team began discussing plans for the wall with the US Army Corps of Engineers and Interior Department.

In his speech Wednesday to a group of law enforcement officers, Trump said plans for the wall were moving forward.

“The wall is getting designed right now. We will have a wall. It will be a great wall and it will do a lot of — will be a big help,” Trump said during a speech before the Major Cities Chiefs Police Association.

What Trump’s border wall could look like

Controversy about the wall has continued since Trump first introduced the idea. Although as a candidate he promised that the Mexican government would pay for the wall, that proposal later came to include the caveat that the US would pay for the wall and would later be reimbursed by Mexico for those costs. Multiple Mexican leaders, including President Enrique Peña Nieto, said Mexican taxpayers would not be funding the project.

The President’s plan to have American taxpayers initially fund the wall has been highly criticized – even by more than a dozen Republican lawmakers.

And some went as far as to say that a wall alone would not do what Trump expected it to.

“No,” John McCain previously said when asked if he thought Mexico would reimburse the United States for the wall. “It’s not a viable option.”

“If you only build a wall, only a ‘wall,’ without using technology, individuals, drones, observations, etc., you’re not going to secure the border,” the Arizona Republican added.