whole foods will give you 10% off cases of anything, and i've heard that they offer pretty good prices on cases of bananas.. almost any market will sell you a case if you ask.. they come in 40 lb. cases (usually about 110 or so bananas i believe)
yup, it's convenient to buy them in 40lb boxes. Find a grocer that will give you a discount for bulk purchases. if you do that, it will take you a few boxes to figure out when to buy them, so that as soon as one box is done, the new one is coming to good ripeness.
In the middle of summer I also have good luck going to a few small local stores in my neighborhood, and since it's hot, their bananas often get riper than they can sell them, and i get huge discounts for taking super spotty bananas off their hands.
I usually buy about 5 bunches every few days at Trader Joe's (in the US) because they are about the same price as buying by the case around here. But I'm thinking about going to the case method. Any store around here will sell cases at a discount, but some are cheaper than others.