Reacting to the estimate, Trump tweeted:

“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. When I do, just like with the F-35 FighterJet or the Air Force One Program, price will come WAY DOWN!”

Trump sent his tweets from his Mar-a-Lago estate in Palm Beach, Fla., where he and first lady Melania are hosting Japanese Prime Minister Shinzo Abe and his wife, Akie.

Aerial picture taken with a drone of the urban fencing on the border between the US and Mexico at El Nido del Aguila, outskirts of Tijuana, northwestern Mexico on January 26, 2017. US President Donald Trump on Thursday told Mexico's president to cancel an upcoming visit to Washington if he is unwilling to foot the bill for a border wall. Escalating a cross border war of words, Trump took to Twitter to publicly upbraid Enrique Pena Nieto. "If Mexico is unwilling to pay for the badly needed wall, then it would be better to cancel the upcoming meeting." / AFP PHOTO / MARIO VAZQUEZMARIO VAZQUEZ/AFP/Getty Images (Mario Vazquez/AFP/Getty Images) People pass graffiti along the border structure in Tijuana, Mexico, Wednesday, Jan. 25, 2017. President Donald Trump moved aggressively to tighten the nation's immigration controls Wednesday, signing executive actions to jumpstart construction of his promised U.S.-Mexico border wall and cut federal grants for immigrant-protecting "sanctuary cities." (AP Photo/Julie Watson) SAN YSIDRO, CALIFORNIA - JANUARY 25: A Border Patrol vehicle sits along the U.S.-Mexico border wall on January 25, 2017 in San Ysidro, California. U.S. President Donald Trump issued an executive order to begin the process of building a wall along the U.S.-Mexico border and is expected to sign an executive order that would suspend the United States' broader refugee program for 125 days. (Sandy Huffaker/Getty Images) A truck drives near the Mexico-US border fence, on the Mexican side, separating the towns of Anapra, Mexico and Sunland Park, New Mexico, Wednesday, Jan. 25, 2017. U.S. President Donald Trump will direct the Homeland Security Department to start building a wall at the Mexican border. (AP Photo/Christian Torres) A U.S. Border patrol agent opens a gate on the fence along the Mexico border to allow vehicles pass in El Paso, U.S. January 17, 2017. Picture taken January 17, 2017. REUTERS/Tomas Bravo (Tomas Bravo/Reuters) FELICITY, CA - NOVEMBER 17: U.S. Border Patrol agents ride ATVs while monitoring the U.S.-Mexico border fence at the Imperial Sand Dunes on November 17, 2016 near Felicity, California. The 15-foot fence, also known as the "floating fence," sits atop the dunes and moves with the shifting sands. Border Patrol agents say they catch groups of illegal immigrants and drug smugglers crossing in from Mexico there daily, despite the forbidding terrain. (John Moore/Getty Images) FELICITY, CA - NOVEMBER 17: Mexico is seen over the U.S.-Mexico border fence at the Imperial Sand Dunes on November 17, 2016 near Felicity, California. The 15-foot border fence there, also known as the "floating fence," sits atop the dunes and moves with the shifting sands. Border Patrol agents say they catch groups of illegal immigrants and drug smugglers crossing in from Mexico there daily, despite the forbidding terrain. (John Moore/Getty Images) SAN LUIS, AZ - NOVEMBER 17: U.S. Border Patrol agents walk over a canal of water flowing into Mexico at the U.S.-Mexico border fence on November 17, 2016 in San Luis, Arizona. The U.S. government has built triple fencing to deter illegal immigrants and smugglers who previously easily crossed the border into the urban area there. (John Moore/Getty Images) File Photo: U.S. border patrol agents on horseback head out on patrol along the U.S. Mexico border fence near Jacumba, California, U.S., November 14, 2016. REUTERS/Mike Blake/File Photo (Mike Blake/Reuters) File Photo: The U.S. Mexico border fence is pictured near the town of Jacumba, California, U.S November 14, 2016. REUTERS/Mike Blake/File Photo (Mike Blake/Reuters) People in Friendship Park in San Diego, California, U.S. are seen behind a fence separating Mexico and the United States, November 12, 2016. Picture taken from Tijuana, Mexico. REUTERS/Jorge Duenes (Jorge Duenes/Reuters) People are seen by a fence separating Mexico and the United States, in Tijuana, Mexico, November 12, 2016. REUTERS/Jorge Duenes (Jorge Duenes/Reuters) A woman talks to her relatives across a fence separating Mexico and the United States, in Tijuana, Mexico, November 12, 2016. REUTERS/Jorge Duenes TPX IMAGES OF THE DAY (Jorge Duenes/Reuters) A woman in Friendship Park in San Diego, California, U.S. speaks with children across a fence separating Mexico and the United States, November 12, 2016. Picture taken from Tijuana, Mexico. REUTERS/Jorge Duenes (Jorge Duenes/Reuters) Tourists in San Diego, California, U.S. are seen behind a fence separating Mexico and the United States November 12, 2016. Picture taken from Tijuana, Mexico. REUTERS/Jorge Duenes (Jorge Duenes/Reuters) Workers continue work raising a taller fence in the Mexico-US border area separating the towns of Anapra, Mexico and Sunland Park, New Mexico, Thursday, Nov. 10, 2016. Last September, the U.S. Border Patrol began erecting an 18-foot-tall steel fence in this area considered very symbolic to immigration activists and also the site where, for the past 17 years, a binational Mass celebrating Mexico's Day of the Dead is held to honor the migrants who have died trying to get to the United States. (AP Photo/Christian Torres) Wooden crosses, in memory of migrants who died crossing to the U.S., lean on the border fence between Mexico and the U.S. in Nogales, in Sonora state, Mexico, November 10, 2016. Picture taken November 10, 2016. Picture taken from the Mexico side of the U.S.-Mexico border. REUTERS/David Alire Garcia TPX IMAGES OF THE DAY (Staff/Reuters) A Border Patrol vehicle drives by the border fence in Tecate, Calif., left, along the metal barrier that lines the border Wednesday, Nov. 9, 2016, seen from Tecate, Mexico. As a candidate, president elect Trump has suggested slapping a 35 percent tax on automobiles and auto parts made by U.S. companies in Mexico, and financial analysts have predicted that the Trump win will threaten billions of dollars in cross-border trade. (AP Photo/Gregory Bull) HIDALGO, TX - OCTOBER 18: A U.S. Customs and Border Protection helicopter patrol flies over a border fence by a bridge between the United States and Mexico on October 18, 2016 in Hidalgo, Texas. U.S. Air and Marine Operations agents fly over border areas, coordinating with Border Patrol agents on the ground to stop undocumented immigrants and drug smugglers from entering the U.S. Immigration and border security have become major issues in the American Presidential campaign. (John Moore/Getty Images) Residential homes are seen next to the fence that borders Mexico, in Douglas, Arizona, United States, October 10, 2016. REUTERS/Mike Blake SEARCH "U.S.-MEXICO FENCE" FOR THIS STORY. SEARCH "WIDER IMAGE" FOR ALL STORIES (Mike Blake/Reuters) Buildings in Nogales, Mexico (R) are separated by a border fence from Nogales, Arizona, United Sates, October 9, 2016. REUTERS/Mike Blake SEARCH "U.S.-MEXICO FENCE" FOR THIS STORY. SEARCH "WIDER IMAGE" FOR ALL STORIES (Mike Blake/Reuters) Pedestrians make their way into the the United States from Mexico at the pedestrian border in Nogales, Arizona, United States, October 9, 2016. REUTERS/Mike Blake SEARCH "U.S.-MEXICO FENCE" FOR THIS STORY. SEARCH "WIDER IMAGE" FOR ALL STORIES (Mike Blake/Reuters) A gap in the U.S.-Mexico border fence is seen outside Jacumba, California, United States, October 7, 2016. REUTERS/Mike Blake/File Photo (Mike Blake/Reuters) SUNLAND PARK, NM - OCTOBER 03: A U.S.-Mexico border marker stands along the border fence on October 4, 2016 in Sunland Park, New Mexico. Workers are upgrading the fence in the area to combat smugglers and undocumented immigrant crossings in the area on the outskirts of El Paso, Texas. (John Moore/Getty Images) MCALLEN, TX - AUGUST 18: A crop-duster flies near a border fence which helps secure the U.S.-Mexico border on August 18, 2016 near McAllen, Texas. U.S.-Mexico border security has become a major issue in the U.S. presidential campaign. (John Moore/Getty Images) Photo Gallery: About 650 miles of fencing is already in place in parts of Texas, New Mexico, Arizona and California, but the border is nearly 2,000 miles long.

During his transition period before being sworn in as president, Trump spoke with executives of Lockheed Martin and Boeing to try to negotiate down the costs of the government’s contracts to build new F-35 fighter jets and a modern Air Force One jumbo jet. After the discussions, both companies, highly dependent on government defense contracts, announced efforts to reduce costs on the programs.

The border wall is a signature campaign promise of Trump’s. He said on the campaign trail that it would cost only about $8 billion, but that seems to have been an unreasonably low estimate.

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