A few quick facts, for those who may not be familiar with The Secure Fence Act of 2006:
The bill was introduced on Sep. 13, 2006 by Peter T. King (R-NY). In the House of Representatives, the Fence Act passed 283 -138 on September 14, 2006. On September 29, 2006 – the Fence Act passed in the Senate 80 -19.
By April 2009 Homeland Security had erected about 613 miles (985 km) of new pedestrian fencing and vehicle barriers along the southwest border from California to Texas.[5]
The Washington Office on Latin America, claims on its Border Fact Check site that the extremely high cost of complying with the Secure Fence Act's mandate-estimated at US$4.1 billion, or more than the Border Patrol’s entire annual budget of US$3.55 billion- was the main reason that it was not fulfilled.[8] In short, Congress failed to continue to fund the project past the initial $1.2 billion procured, in order to finish building the fence.
https://en.wikipedia.org/wiki/Secure_Fence_Act_of_2006
At first blush, 4.1 billion does seem like a lot of money. I would point out, however, that Congress routinely tosses around billion dollar figures for all sorts of things (Over half-a-billion was spent to fund Solyndra alone, for example, with nothing gained to show for it). I think 4.1 billion sounds like a lot of money to those who prefer the wall not be built, less so to those who want it erected.
What happens next remains to be seen.