I found the pupusas relatively thin and uninspired, with the cheese variety the tastiest on its own. The pork filling is a little like Carolina pulled pork, but stretched instead. The Salvadoran quesadilla is, and has always been, an eggy cheese bread with sesame seeds, typically reserved for Sunday dessert. Some other dollar desserts are rice pudding and pineapple upside-down cake. La Pupusa Guanaca also has weekend specials like big soups and tamales.
Service is a guy behind the counter, atmosphere is bright lights and whoever else walks in.
Both these restaurants show that cheap is not necessarily slapdash or boring.