I am not sure if this is a bug or something that I will just have to get over, but when using an anvil, if I add my enchanted axe to the first slot, and a non enchanted axe of the same material to the second slot, the cost is relatively small, around 2-4. However, when I reverse these two items, the enchantment cost sky rockets to 18-24 enchantment cost.
Duplicate of MC-3880 - If you have not, please use the search function in the future, to see if your bug has already been submitted. If you could not find the original report, please comment with the keywords you searched for.