Wandering around República, the area south of the Alameda (Avenida Liberador Bernardo O'Higgins) is hungry work. It's an area with a high concentration of universities and institutes (technical schools) and as such, there are a host of affordable eateries.
The best sandwiches in this part of town, and in fact, some of the best food is to be had at Cheveríssimo, which means "way cool," a Peruvian sandwich shop with giant portions of tasty suckling pig, turkey and other options, served with the sauce of your choice, including olive, spicy and a mild, creamy huacatay sauce that melts on the tongue. You can also add shoestring fried potatoes to your meal, and although it's not on the menu, there's an excellent vegetarian sandwich with a couple of eggs (if you like), tomatoes, avocado and lettuce. The bread is homemade and light and actually holds together to eat with your hands, though most people will prefer a knife and fork.
The smallest size, which is plentiful for most appetites is around $4 US (2,100 Chilean pesos). Drinks are the standards with the addition of a a few Peruvian favorites, like Inka Cola.