Where can I get some extra heavy-duty aluminum foil without having to pay a lot? I can easily find online sources, but these (1) tend to be for restaurants, (2) tend to come in bulk (like a 2,000 mile roll), and (3) tend to cost much more (like $70, $100, $200).

Some people recommend extra heavy-duty aluminum foil for your survival kit. All I can find is heavy-duty in the local supermarket. I don't know how big of a difference it makes. I'm also surprised by how hard it is to find extra heavy-duty. Any ideas?