NPC Located as the previous poster stated, in Aht Urghan Whitegate at (F-9). She is an Elvaan named Rubahah who runs a stall located to the east of the man with his automaton entertaining a crowd.
Price list:
Millioncorn: 48g
Imperial Flour: 60g
Imperial Rice: 68g
Coffee Beans: 316g
(these prices may vary for your fame level but not by much i guess)