I don't think I'd do a lower- since without forging dies a cast lower could be porous, and aluminium cans are of indeterminate alloys.
0% forgings are available for $25-30, and 80% for less than $50.

But some other pieces you want to copy or create- lost foam casting of Al is not too hard, so if you can make it out of foam, you can cast it in Al (within reason)
This forge would also get hot enough to melt copper, bronze or brass. Hot enough to forge/form steel, but probably not to melt it- depending on the alloy.

you could always cast an anthill.. that really pisses off the hippies: