El Quinque was recommended to us by the owner of the apartment that we're renting on Oaxaca and we we've been back every day since the first... The food is fantastic value, especially the menu of the day, at only 50 pesos. Other dishes range from 70 to 140 pesos, not incredibly cheap by Mexican standards, but very cheap for the quality of the food.
All dishes, including the menu of the day, come with drinks (jamaica (hibiscus) or lemon), rice or potatos and salad. Anything extra we asked for (extra salad, drink, bread and even a few prawns beside our steak) was no problem and was never even charged for. On our third visit Estefan even insisted that we try a little of the local mezcal on the house!
Especially recommended are any of the menus of the day (tasty and cheap), the camarones ajillo (prawns with a lemon, garlic and chilli sauce) and the arrachera (see http://en.wikipedia.org/wiki/Flank_steak for details). I've also heard good things about their burritos and hamburgers, so I'm looking forward to checking those out.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.