¡Prefiero Gratis!
One seldom discussed issue is that it is so hard to make it all the way down to SCdLC if you stop at all those tempting places along the way. They are difficult to leave.
The MAJOR issue with the city of Oaxaca is it is way the hell and gone out of the way. Coming or going, it involves a lot of ordinary blah scenery and overnights, unless you backtrack up and back from the coast. Unless you have 180 days to burn and pocket full of pesos for fuel maybe Oaxaca deserves its own trip, with Tehuacan, Puebla, and maybe Toluca and Valle de Bravo as points of interest.