Assuming they are in fact aluminum, that would technically be either investment cast or (more likely) die cast -- in the latter case, it would most commonly be an aluminum-zinc alloy in the Zamak family (generically called "pot metal" but when correctly alloyed is much better than the reputation pot metal has). Similar aluminum/zinc alloys were used for decades for things like car door handles and window cranks, and are still used for metal drawer pulls and cabinet handles.
Characteristic of Zamak family alloys is that they're much heavier than aluminum (density is close to cast iron), but avoid the "crystalline" look of pure zinc. The ability to die cast to high precision makes these alloys very popular in cost-efficient manufacturing; they'll stand up to light duty use in power tool gears and pretty heavy use in housings, for instance, and cost pennies on the dollar compared to parts that need to be machined before use because they can be installed and used as-cast.
That's the Riga-specific gray version. The black one actually linked is GBP 69 including a "coffin case" and set of (optional) light trap felts. Still high compared to used plastic ones on eBay, but perhaps not excessive for brand new, universal fit (except possibly early Riga models, as witness the same seller's alternative model) metal cassettes.
