Unbind cost of upgradable items depends on item quality. For example most uncommon artifacts (at level 1) could be unbound for 10 tokens and mythic artifacts (at level 140) could be unbound for 50 tokens. So I can unbind artifact for 10 tokens and then upgrade it to mythic instead of unbinding mythic for 50 tokens. Upgradable items must have same unbind cost on all ranks (same as on max rank).
1
Comments
case 1:
bound mythic -> 50 unbound token -> unbound mythic
case 2:
bound green -> 10 unbound token -> unbound green -> refined for 1RP -> bound green -> more refine -> bound mythic
It makes perfect sense for the unbind token difference between different level. If they are the same price, nobody will spend to unbind anything in green (the beginning) but just do it right before it needs to be moved to alt or be sold in AH.