You misunderstood :) Enchantment consists of two stages:
1) You fill the enchantment scale with ANY ingots. "Any" is usually aluminum :)
2) You enchant the pickaxe with the material you need.
And the prices increase separately. 50 is the first price for filling. 10 is the first price for the enchantment of each individual metal. Actually, that's why aluminum is spent on filling. I don't think you'll find ten thousand platinum :) But a tenner for enchantment is quite enough.