Peruvian food is becoming more common in the capital, and plain-Jane Status (Virrey Cevallos 178, tel. 011/4382-8531) is one of the best budget options, with home-style central Andean dishes such as ají de gallina (chicken in a walnut sauce over rice, with potatoes) in the US$5 range. Spicy items and garnishes, such as papa a la huancaína, are also available.
According to Buenos Aires Herald restaurant critic Dereck Foster, Buenos Aires [1]’s best Spanish food comes from the restaurant at the NH City Hotel (Bolívar 160, tel. 011/4121-6464).
Other Spanish/Basque seafood options include the classic (and author favorite) 
Laurak Bat (Avenida Belgrano 1144, tel. 011/4381-0682, www.laurakbat.com.ar [2], US$10–20).
Near Monserrat’s western border, San Cristóbal’s Miramar (Avenida San Juan 1999, tel. 011/4304-4261) is a reliable rotisería (deli) that’s also a decidedly unfashionable bodegón restaurant that’s ideal for unpretentious lunches or dinners with poised service. Prices are moderate, even low, for items such as gambas al ajillo (garlic prawns) and lechón (roast pork).
Links:
[1] http://www.moon.com/destinations/argentina/buenos-aires
[2] http://www.laurakbat.com.ar