“a patrol every mile for 700 miles 24/7 would cost less than $250 mil.”
It takes at least five folks (five shifts) to fill one position 24x7 (40 hours a week each). Six allows for easier scheduling of leave, sick leave, and training.
Border Patrol Officers must be trained and equipped, and each carries a relatively high overhead cost for retirement/medical benefits. Each costs well over $100K/year to have on staff.
If you have just one person per mile, what will they do if 10 immigrants make a run for it at once? 100?
In practice, it turns out that people are the most expensive component of border security, infrastructure is the second most expensive, and technology is the cheapest. Regardless of the price differences, to achieve effective outcomes, you need all three.
I preferred the minute men.