Depends on how specific the key is and what make it is. If it's a VW or Mercedes, they will sometimes have individually grooved keys for each car, hence they take a bit more time to replace/manufacture. That also means it's expensive versus other generic keys.
Agree with Kevin. While keyless remote entry seems to be the norm as well as keyless ignition systems (although that feature leans more to higher-end models), there's a vast majority of cars out there that still require the good ol' key and lock. I always recommend getting a duplicate car key as soon as you get your hands on the master key. It saves you the trouble of having to pay out a hundred or so dollars for a new from the dealership.
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