We could expend $16 million per mile for the entire 2500 mile length and still save more than the $41 billion a year the illegal aliens cost taxpayers.
And if we could seal the 2000 mile Mexican border, there is still the remaining 103,000 shoreline and other land borders. Remember the boat people?
And most drugs are brought in by plane, sea and by bribing guards at crossing points. Those routes would be used to smuggle illegals if the land borders were sealed.
Trying to seal the border is a useless exercise in wasteful spending. Only token efforts will ever be made, and only to appease a small but vocal group that doesn't recognize the futility of the exercise.