The San Francisco to Mexico City route is one of the most expensive routes down south. Fares usually hover around $500 per Round Trip (the flight is just about 4.5 hours one-way) and often hit $1,000 (!) for short notice bookings.
There are occasional sales – usually from American Airlines but now AeroMexico is putting the route on sale. Several dates in the next weeks are just $161 – here are samples:
Mexico City is a surprisingly urban city with fantastic food and friendly people – in fact Mexico City is one of my favorite cities in the world.