Mexican Tourist Permit Is An FMT, Not A Visa
You need a Mexican tourist card (FMT) to Travel Mexico Beyond the Border
You don’t need a Mexican visa to travel to Mexico as a tourist. You need a Mexican tourist card, called an FMT. Mexican tourist cards (not visas) have not been free for years (except for a 7 day permit). Although the cost of your Mexican tourist card (FMT) varies according to the peso and does go up periodically, a Mexican tourist card will set you back about $22-$25. I stopped giving the exact price in pesos as it changes, the exchange rate changes and the difference is miniscule. You do not need a Mexican tourist permit for Baja. Your car permit to drive in Mexico is another document you will need if you are driving in Mexico beyond the border.
Once again (2010) a 7 day FMT tourist permit for Mexico is free. This changes periodically.
Migracíon has a record all tourist permits. Be sure to turn your tourist card (FMT) in to a Migracíon office near the border. Finding these is a challenge, but worth it. Hacienda kiosks are usually near (but not on) the bridge or border crossing. The toll-takers on the bridge cannot take your tourist permit. Since you have to turn your car permit in anyway, find the Hacienda office and turn them both in at the same time. How, you ask? Ask at the 21 kilometer (this is an approximate number. At some point there is a customs/immigration checkpoint -- for those entering Mexico and sometimes for those leaving). If no one is on your side of the highway, I would park, walk across the highway (if there isn't a lot of traffic) and ask the guys on the inbound checkpoint where it is. The next best way is to ask a cop, or better yet, a highway patrol officer for, La casita por los tamites del autos por extranjeros.
If you do not turn in or cancel your FMT or tourist card, you will incur fines and be denied entrance to Mexico later. See my story about the fines you will pay if you don't return your FMT tourist card. The solution is also there.