$21 Billion for a wall is nothing for a country as large and successful as the USA. It's pretty much pocket change that could get lost under a sofa cushion and

$21 Billion for a wall is nothing for a country as large and successful as the USA. It's pretty much pocket change that could get lost under a sofa cushion and not be missed. Our federal budget for 2015 was $3.8 trillion. Spending half a percent on a wall is not a problem. $21 Billion is about 0.1% of our GDP. Note that even Mexico has a GDP of $1.3 trillion (in US dollars), so they can in fact pay for the wall. Even for Mexico, the wall is kind of affordable. Walls are cheaper than highways. Notice that we have numerous highways running across the USA. Dealing with these people is costing us 3 to 6 times as much EVERY YEAR as your figure of $21 Billion. If the wall were flawless, we'd get a payback in just 2 to 4 months. I agree on the detection though. In most areas, the proper physical barrier is probably a fence every half mile for a couple miles, for a total of 5 fences.