Quick googling would suggest that steel used be be ~$550/tonne pre-pandemic. An empty 20' container weights 2.3 tonnes, a 40' container 3.9 tonnes. So raw steel cost would be $1300 for a 20' container and $2100 for a 40' container (completely ignoring that I might be looking at the wrong grade of steel, or other ingredients like the antifouling paint).

I believe they meant the cost to ship a container full of goods across the Pacific rather than the cost of buying an actual container.

Source: My company imports

No, the 20/40 feet containers were costing that. Amazon are creating a new category of containers to match their trucks.

Prior to the pandemic, steel was $400-600 per ton.

Yep. I once had a whole bunch of stainless steel tanks fabbed in China, loaded into a container, and shipped to us on the East Coast. Shipping was ~2.5k for this giant container.