Inexpensive metal boxes or cabinets for housing electronics?

I’m trying to do things without spending lots of money so I was looking at empty computer cases, metal filing cabinets and metal cupboards from Ikea. Ideally I need something that has low flammability and can be easily modified using hand tools. Aluminum or fiberglass would be ideal materials but everything I’ve seen is steel.

I haven’t reached the DIN rail stage yet. Everything is just proto boards lying flat horizontally.

I am a fan of repurposing all sorts of stuff. I had (for a few years) a salvaged jockey box from a bus as an outdoor enclosure. I found an actual NEMA approved outdoor box that eventually replaced it when i was digging around in a Habitat for Humanity reclaim store. I have a node cabinet out at my gate that is a steel underbody truck tool box. It would be more ideal to have aluminum or fiberglass for sure but those options are few and far between. I have found that places like Craigslist (or Gumtree for the non-continental folks) is a good place to find cheap items that can be repurposed.