Casa de los Amigos

That is the name of a guesthouse in Mexico City that provides very inexpensive accommodation and other programs in what its Website (www.casadelosamigos.org) describes as a "diverse and open social justice community." Amigo means friend in Spanish, and this attractive place is run by the Society of Friends, otherwise known as Quakers (those delightful folks who brought you Pennsylvania, Richard Nixon etc.).
It has men's and women's dormitories with 12 beds each, and while prices are not given on the Website I learned from another source that a bed can cost as little as $10 a night. It attracts not just tourists, but also refugees and volunteers of various ages and backgrounds. The Casa is drug, alcohol and smoke free.
I hesitate to say much about Mexico City, since I haven't been there for close to 20 years. It used to be one of my favourite places to visit, in a beautiful setting surrounded by volcanoes and with pleasant weather most of the year. On my first visit you could still see snow-covered Mt. Popotecapel towering above the city, but now it is usually shrouded by pollution.
 From what I have read Mexico City has become a lot more dangerous in recent years. Still, it has plentiful attractions including the wonderful Archeological Museum, Chapultepec Park, the zocalo with its beautiufl cathedral built near ancient Aztec ruins, and the large Aztec site nearby at Teotihuacan. The Mexican people are another reason to visit--in general they are very welcoming to strangers.
Still, Mexico is an enormous city and one where you may want a quiet retreat at low cost. For that, the Casa de los Amigos sounds ideal. It also offers volunteer opportunities, particularly for fluent Spanish speakers who are willing to commit to serving for nine months or more, and some shorter-term openings.