I spent a couple of decades in Asia. We used to import chopper engines, make frames from iron tubing and build the rest of the bike from salvaged goods... I just loved the garbage dumps/ salvage yards there. They had entire industrial areas just selling salvaged junk imported from Japan.
Gold mines
Here in Finland the socialists just do everything for face value. They created this huge government sponsored network of recycling centers, but they don't have a single location where someone could get recycled materials. They just opened a chain of flea markets that killed the market for all the real second hand shops, and got a couple of artists to make lousy stuff from recycled materials. They pride themselves for progressive recycling but its really a freak show.
Here is an interesting product. Aluminum shelf for greenhouses, 40kg weight limit. It has 6 600mm extrusions ready to use.
With slight modification this could be used as a frame hung from above. It would be a really cool option for a 2x4 in a room where you could screw it into the wall. How about a 2x4 vertical with plants in two layers
Now I found an angle extrusion which seems a little flimsy, but costs 2.20e for 3m... its just ridiculous, and I think sufficient for softly driven strips (gen 2's at around 950mA)
So I finished my fixture. I went to buy the 2.20e/3m alu extrusion, it was 0.6mm thick, and so weak that it just rolled up when I tried to drill a hole into it.
I felt it got pretty solid after I glued the strips to it, I'm already sure it works, although its not torture proof. Heatsinks for 6 4 foot strips were 6.60, and the frame elements 1.90e. So besides the drivers and diodes the build was less then 10$
I noticed that nailing plates are awfully cheap. With some thermal adhesive, they could make a cheap and dirty heatsink for something like $0.40/ft, if bought by the box. Probably not good for hard driving, but better than nothing with regular PCB strips, I would imagine.
Steel. They are very thin, though, and would cool alright, for what surface area they can add. Also, they could double as mounting aids.
While you wouldn't design a heatsink from steel, sure, the LED package to board and board to heatsink junctions are going to dominate with lower overall temperatures, and almost any thin metal will be a substantial improvement.
