In Salamanca, for every drink you order in a bar, you get to choose any bar snack you want for free, which means that you can eat on the cheap. To do this, you have to stand at the bar, although some places have tables close to the bar where you can sit (as long as the tables don't have tablecloths; if they do, it means they are reserved for people who plan to order from the menu). If you order wine, they'll ask if you prefer Ribera del Duero or Rioja. Both are very good. The first is smoother and regional, so we recommend trying it.
One of the most famous bars for tapas is Cervantes (Plaza Mayor 15). Their specialties are stuffed omelettes (we recommend the one with tuna) and "huevos rotos" (literally "broken eggs") with "gulas" (young eel) or meat (tapa + glass of wine: 2.50€).
Very close by is the also famous Bambú (Calle Prior 4, southeast exit of Plaza Mayor). Their signature dish is grilled meat (12.25€ for a plate of ribs). As for tapas, the croquettes and "bombas", in addition to the ribs, are also very good (tapa + glass of wine 2.10€).