The following is an excerpt from 1984:
In the low-ceilinged canteen, deep underground, the lunch queue jerked slowly forward. The room was already very full and deafeningly noisy. From the grille at the counter the steam of stew came pouring forth, with a sour metallic smell which did not quite overcome the fumes of Victory Gin. On the far side of the room there was a small bar, a mere hole in the wall, where gin could be bought at ten cents the large nip.
Can we say a large nip? What's the difference between a and the in such cases? Can we also say per large nip?