This political season has featured a lot of loose talk about building a wall along the U.S. southern border. A really big wall. (And while many candidates have talked about a wall, there has been notably less talk about the fact that illegal crossings of the southern border are at historically low levels).

Of course, this isn’t the first time politicians have fixated on the idea of a border barrier. Previously, the preferred solution was more in the form of a fence studded with surveillance cameras. The Secure Fence Act of 2006 built a barrier along more than 650 miles of the border at a cost of $2.4 billion. (And, by the way, the border with Mexico is 1,989 miles long, although some of it is controlled by natural barriers. But most people talking about a new physical barrier state the wall would be 1,000 miles long.)

Then, a few years ago when the political climate seemed to be turning to the possibility of substantive immigration reform, those who vehemently disagreed with that idea insisted that “border security” must come first. The debate turned to a smorgasbord of ideas to militarize the southern border at the enormous cost of $12 billion. Included on the menu of bad ideas was an outdated Department of Homeland Security wish list of technologies for about $4.5 billion. Legislative language opined that an additional $30 billion would be required for the deployment of additional Border Patrol agents.

So how much would it cost to build 1,000 miles of the kind of 40 foot wall that is so frequently being discussed? Recent estimates by a former estimator for a large national construction company put the cost at about $25 billion. This estimator also predicted it would take 40,000 workers a year, laboring for at least four years.

Of course, these estimates are based on work done on time and on schedule and anyone who has been paying attention for the last 50 years knows that in the context of the government contracts system, costs can go up and schedules often lengthen.

But, for the sake of argument, let’s agree that the U.S. government would be able to build the wall for this price and on a four year schedule. The budget request for the Department of Homeland Security for the coming fiscal year is $41.6 billion. This means we would have to increase the DHS budget by about 15 percent per year for at least four years to afford just the construction of the wall. Add to that the unknown but undoubtedly large cost of more Border Patrol agents to monitor the sensors that will be part of this wall. Let’s face it, no federal department, not even the Pentagon, is receiving budget increases like that in the current fiscal climate.

Militarizing the border and building a 40 foot wall for 1,000 miles, even if it was likely to keep us “safer,” isn’t affordable. With a $19 trillion debt, it’s time to stop talking about an unworkable, unaffordable idea.