In places like Mazatlan, PV, Guadalajara, etc--places where gringos congregate--find the established resident gringo community (the tourists won't know) and ask around. Believe me, this is a matter of considerable interest to expats, among whom you may find retired doctors and dentists and others from the health care industry. Guadalajara and Mexico City are said to have excellent hospitals with inexpensive treatments, even after they have raised the rates for gringos.
There are bulletin boards for Mazatlan, Puerta Vallarta, Morellia, Tepic, and many other places. Try Mexico Connect, too. Go back through the archives for each board and look for questions similar to yours. This is also a popular topic on boards for Panama and Costa Rica.
This is something that you want to do your homework on BEFORE you need the services. I don't think I would just wander over the border to Tijuana looking for a doctor when I need one all of a sudden.
There is a cross-border health industry down by Yuma, AZ. Scott Burns wrote about it a couple of years ago. The locals in Yuma seem to know that center very well. People like RV'ers come from all over the country to go there for health care.
Lonely Planet published a pocket book, "Healthy Travel--Central and South America" (included Mexico, as I remember). It was intended for travellers, but there was a section on books about health care south of the border.
Then there is always Thailand, where they are establishing health care as a tourist destination. Billy and Akaisha have links to one center on their web site.
This is something I am seriously interested in myself.
Ed