[Tuna-Fish]

Aluminum vs Copper is not that simple. Aluminum has worse conductivity for the same area, but area is in no way fixed. And aluminum has actually better conductivity than copper for the same weight. You just have to make the cables a bit thicker.

[anamexis]

I think the relevant metric here is conductivity for the same cost.

[II2II]

It may come down to cost, but other physical properties enter the picture. For example: thermal expansion is an issue for overhead power lines, along with how ductile it is.

In other cases it is more important to reduce resistance, not so much because of the power loss but because of what the power loss means: the generation of heat that may be difficult to remove.

Of course you can get around those problems at extra cost, but it is more than a straight up comparison of the material cost of the conductor.