Near Parque El Calvario a guy selling the real pupusas salvadoreñas is installed. Prices are around 12Q to 18Q, depending on size. The 12Q pupusa is maybe 15cm and 18Q 25cm.
And listen to this crazy history. Last time I visited the place I could observe a big big hamburger for 10 persons. The crazy price was 150Q for one hamburger. Inside their was two pounds of meat, papatoes, cheese, tomatoes, dressing and more. If you are very hungry maybe it is for you. What do you think?
You can taste other options, buying pupusas at 7Q in Central Park all nights, but I prefered the 18Q one.