SDB has written a long piece about the effectiveness of Israel's wall around the West Bank, and it makes me think we could use one of those here in America.
According to The Electronic Intifada (which I assume will give pessimistic estimates), Israel's wall will be about 400 miles long and cost in the neighborhood of $2 billion -- a cost of $5 million per mile. Our border with Mexico is a bit under 2,000 miles long, so an American-Mexican Good Neighbor Wall shouldn't cost more than $10 billion. Not an inconsiderable expense, but just think of all the manufacturing jobs it would create.
For those who'd claim such a wall would be "racist" or "isolationist" or some other such nonsense, just imagine how many more legal immigrants we could let in if we're ever able to stem the flood of illegals. While you're using your imagination, think of all the lives we'd save.
As a further note, such a wall would be good incredibly good for Mexico as well -- until American financial life support is cut off, Mexico's corrupt kleptocracy will never be reformed and the country will be doomed to stagnation. It's time to shake up the status quo.