I like the idea of having:
Upgrade 1-5: Common Ingots
Upgrade 6: Rare Ingots
Upgrade 7: Ultra-Rare Ingots
Upgrade 8: Epic Ingots
Upgrade 9: Legendary Ingots
Upgrade 10: Mythic Ingots
Suddenly the more common ingots get used way more often and the ridiculous rarity of Mythic Ingots get scaled properly to how many times they need to be used. (I.E. Each Mythic weapon only needing 10 Mythic Ingots).