If you'll be driving in Mexico, you should know that Mexico's Secretary of Communication and Transportation provides an excellent on-line tool for planning your route. The "Point-to-Point Routes" tool will allow you to see the route you should take, along with the driving distance and tolls you'll have to pay, as well as an estimate of fuel costs.
All you need to do is select your city and state of origin (within Mexico) and your destination city and state and click the "Find Route" button at the bottom of the page. You may also select intermediate cities you would like to visit along the way.
Find the tool here: Point-to-Point Routes.
