Although there are motorways/relatively new toll roads for a good portion of your journey, I would not recommend driving it, especially if it's just a single car.
Alternatives are: 1. buses (check the bus thread) that you can probably catch directly from MEX, 2. flying MEX-OAX on a separate ticket (on Interjet for example - ~USD110 round trip), 3. Volaris flies TIJ-OAX; it's relatively easy to get to TIJ from SAN, so that may be an option.