This is the leanest time of year for people looking to buy Corns from shops - only the tail end of last year's hatchlings will be left. Supply and demand dictates that if you're a shop and you have a lot of customers after a few products, then the price is likely to go up.
As for breeders, well, this is just before the breeding season. They'll be taking a long hard look at the Corns they have and deciding which really are keepers and which have to go. If they're pushed for space, the price is likely to go down a bit in order to move the animals out and make space for the ones they really want to hold onto.
So if you want a bargain this time of year, buy direct from a good breeder and don't bother with the middle men!