Casting sand isn’t cheap, molds definitely aren’t cheap and don’t last forever requiring skilled tool and die guys to repair/replace them, machine time definitely isn’t cheap, the machines themselves are incredibly heavy and very expensive, and tooling for those machines aren’t cheap.
I’m running some castings right now… we’re at $165 in material and labor before it ever touches a lathe or mill (we pour our own castings, some investment some sand cast). And that’s assuming this batch of castings is good, sometimes they’re full of porosity and we have to scrap out a ton of parts.