Booked TIJ-(MEX)-MTY rt for $242
My thanks to jfkeze. Spent a little more money to avoid weird arrival times at destination, stopovers, or origination airport.
Monterrey looks good for a two night trip. I can stay the first night at an airport hotel and eat at the nearby Il Castello di Frabo. It seems to be a world-class Italian restaurant with reasonable prices. Second night near Macroplaza and Barrio Antiguo. The city history museum looks good, too. A full day is enough for the highlights. MEX or GDL would be worth longer stays. Maybe next time.