The Cost of repairing a Diamond Pick Axe with Unbreaking III, Silktouch I, and Efficiency IV was too expensive with 37 levels available. However a Diamond Pick Axe with Unbreaking III, Efficiency V, and Silktouch I only cost 1 level and a couple of diamonds to repair. Even though this time had more enchantments... level V efficiency vs Level III.
Comments 2
The cost is dependant on how often that item was already used on an Anvil, see http://minecraft.gamepedia.com/Anvil_mechanics
Maybe it's not incorrect and just inconsistent?