U.S. Customs and Border Protection announced the selection of four construction companies to build concrete prototypes of the wall President Trump plans to build along the border with Mexico.

Each prototype will be 30 feet tall and 30 feet wide, and cost between $400,000 and about $500,000.

None of the companies are based in California.

The four companies are Caddell Construction of Montgomery, Albama; Fisher Sand and Gravel/DBA Fisher Industries of Tempe, Arizona; Texas Sterling Construction of Houston, Texas; and W.G. Yates & Sons Construction Company of Philadelphia, Mississippi.

Trump last week said that he was prepared to shut down the government if lawmakers did not approve funds for building the "big, beautiful wall" he promised during his presidential campaign.

Trump initially insisted that Mexico would pay for the wall, but its leaders have flatly rejected that idea. Now the president wants Congress to fund it.

The Department of Homeland Security has estimated the cost of the wall at $21 billion. An MIT study puts the price tag at $38 billion.

The acting deputy commissioner of U.S. Customs and Border Protection, Ronald Vitiello, called the contractor selection "a significant milestone."

"This is the first tangible result of the action planning that has gone on. This is the use of the resources we had available for this year," Vitiello said in a Washington, D.C., news conference. This stage of the border wall project will be paid for with funds already appropriated by Congress for the current fiscal year.

The actual prototype construction will begin in about two weeks following discussions with the selected contractors about scheduling. They will have 30 days to complete their prototypes. Homeland Security officials will then take 30 to 60 days to test the prototypes to see if they can be penetrated or otherwise compromised.

Four more contractors will be selected who have proposed to build prototypes with materials other than concrete. That announcement is scheduled for next week.

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