Posada La Casa de Carmelita (Calle Dr. Navarro 15, tel. 967/678-9975, posadacarmelita [at] yahoo [dot] com [dot] mx, US$10 pp shared bathroom, US$12 pp private bathroom) is a friendly family-run place with spic-and-span rooms and a great location. Rooms with shared bath are pretty dark, but the others open onto a corridor with terrific views of the city and surrounding hills. Meals are available for US$4 apiece. A handful of groups use Carmelita’s regularly, so try calling ahead to be sure there’s room.
Rooms at Hotel San Martín (Calle Real de Guadalupe 16, tel. 967/678-0533, www.travelbymexico.com/chis/sanmartin , US$20 s, US$25 d) are very simple and spare, with twin beds, tile floors, and clean private bathrooms, all looking onto a narrow interior patio. It’s far from charming, but not unpleasant, and the location couldn’t be more central—just a half block from the zócalo. Cable TV and free Internet access are an added bonus.