I personally go down to the ol' reptile store and buy a month's supply at a time. If i was to make a bulk order it would have to be in advance. In my case its a little funny because I have an adult and a baby so it would be a little awkward to have a big ol' bag kicking around in my freezer with the pizza pops.
I usually pay around 75cents per pinky and a 1.20 per mouse. I heard its cheaper to buy in bulk but I'm not too fond of mass frozen mice, they tend to lose limbs and look funny after a while.