The Great Wall of the United States

So, after much laughter and jokes from critics claiming it was virtually impossible, it would appear that Donald Trump will get his wish and there will be a physical wall constructed between the United States and Mexico. However, it would appear that the wall is going to cost considerably more than what was initially thought with Reuters reporting that it will cost approximately $21.6 billion, instead of the $12bn suggested by Donald Trump during his campaign. 
The wall will be 2’000km in length, adding to the 1’046km of already fortified borderland. The details have been unveiled by Reuters, after they reportedly managed to attain access to a report commissioned by the Department of Homeland Security. 
The wall was one of the most prominent pledges made by Donald Trump throughout his campaign, promising to deport all illegal immigrants and to give the jobs left behind to citizens of the United States. He also claimed that the U.S. taxpayers would pay for the wall and would later be refunded by Mexico, something that Mexico has unsurprisingly profusely denied. 
One of the main costs with building the wall is the need for the government to buy any private land which would be in the route of the wall, something which will obviously cost a considerable amount of money when the seller knows the reasoning behind the purchase. 
Already the US government has begun seeking waivers to address environmental laws on building in some areas, the report indicates. It also depicts the government as having already begun working with contractors, and planning steel purchases. The current figure being estimated for the cost of the wall also doesn’t cover the extra charged that might be incurred when you consider the extra effort and construction needed when building on immovable objects, such as mountains. 
According to Reuters the report said the first phase, costed at just $360m, would be modest, targeting sections covering 42km near San Diego, California; El Paso, Texas; and in Texas’s Rio Grande Valley.