Pacante's fastfood café
Jr bolognese 464. simple and cheap burgers, with a friendly owner who likes to talk to gringos.
street food
For fast and cheap street food try one of the stands at the south-east corner of the Plaza de Armas.
The restaurants you find all over town that are used by natives offer a full menu soup, a choice of 3-5 main dishes, and a drink for 5-10 soles.