copper is 3-6x more expensive than aluminum...
And copper is one of the best conductors, that why they use it for electricity, and heating elements. The best conductor is gold, but that's to expensive to use.
I'm not sure where the idea that gold is the best conductor came from, but it isn't true. Both silver and copper are better conductors than gold(both electrical and thermal conductivity).
Aluminum has about half of the EC of copper and just over half of the thermal conductivity.
Gold seems to be used on some things because it resists oxidation.