Apparently you really were toying with the numbers instead of checking them, since your math is wrong. At 4 agents per mile and 2,000 miles, that's 8,000 agents, and at $40,000 each, that's $320 million per year. I think that's an overestimate, and, in any case, we're spending some of that money already (ineffectively), but it still is a drop in the bucket. Remember that each illegal immigrant is costing society about $10,000 per year, net, just based on rudimentary benefits and services that local and state governments have to provide. On top of that, they take jobs from our own citizens, which creates unemployment and the highly corrosive effects that come with unemployment (i.e. depression, erosion of skills and discipline, crime).