I've had coffee here a couple of times. Their americano (straight, no sugar/milk) is strong, delicious and very cheap. They also have frozen varieties like Mocca that are also good. Next door you can find a place that specializes in selling equally cheap churros. For a great coffee-break, combine the two and enjoy them while sitting on a bench in the Coyoacan main plaza just a block up the way. Total damage less than 30 pesos.