Hotel Casa Grande
Ojeda No. 10
Is the cheapest digs in town $15 for a single with shared bath. it is a 400 year old building just off the plazuela and is about a block from santa prisca and the zocolo. rooms are arranged around a courtyard, some are great, some are a little scruffy with semi-functional bathrooms, so ask to see a few. the rooftop terrace is really great for relaxing and looking out at the city.
Mi Casita
Guerrero 1
Located off the plazuelita. Lovely inexpensive hotel with great views run by a nice family.
Hotel Santa Prisca
Cena Obscuras #1
For a little fancier accommodations the Hotel Santa Prisca is a beautiful place with a fountain and lush court yard.
The Agua Escondida is right on the Zocalo and has a nice pool. Ask for the cheaper rooms at 350 Pesos.