When creating a weapon that is +2 to hit +2 damage, how much magical power is needed? [closed]

if a master weapon smith is making a +2 to hit, +2 damage axe strong enough so that it can hold a high level spell enchantment, approximately how much magical power should be required to be infused in the forging? The intended weapon is a reforging and re-enchanting of a legendary weapon which was broken fighting & defeating the champion of Belial, Arch devil master of the 4th level of the nine hells. It will target fiends & celestials (hopefully).