There was a taco stand around the corner from where I was staying in Mexico City. They would be there all day and all night - until 3am, if I remember correctly.
Each taco is rather small - I typically engulfed one in two big bites - which means I usually ate between 6-8 tacos to fill my stomach. Oh how I would afterwards. And they only cost $0.25-$0.30 each.
First a tortilla is filled with shreds of beef, chopped sausage, onion and parsley. Then you simply choose your sauce, top it off with a squeeze of lemon and you're set.
I must stop writing now... my saliva is dripping onto the keyboard.