Not to mention that not all rental companies will necessarily allow rental cars to be taken across the border. It was an option last week in a Texas border town, but a few years ago in Arizona it was a definite NO-NO, at least the company that I found over the internet (don't recall, not even sure if it was a major chain, though last week it was).

And be careful driving in Mexico, I hear that as tourist are getting more nervous about traveling the cops are more hungry to fine the few remaining visitors

EmailKid