If there is a 5 marked out in their trading list, this is an intentional feature. Minecraft introduced supply and demand economics, and if a villager constantly 'sells out' of an item, they raise the price. If this new price is paid, and again, the sell out, it goes up even more. To get the price back to 'normal', just don't buy that item from that villager for a while. I think it takes a few in-game days for this to go back to the original price.
Sorry, first part didn't make sense. If you see one number crossed out, and a larger number next to it, than this is what I mean. If 2 different villagers have 2 different prices, this is also intentional. Try to get the higher cost one to get another profession!