I purchased a used certified pre-owned 2012 Elantra limited (without keyless start) 2 days back and the dealer just gave me 1 key for it. I tried asking them multiple times if they have another key, but they are not answering to it.

I want to have an additional key incase if this one gets lost ever.

Where can I make the duplicate key for cheap?

 

Any quality locksmith that handles automotive keys.

 

I just brought a CPO hyundai elantra last week from a hyundai dealer and they just gave me 1 key, whereas on the CPO hyundai checklist 5 keys are mentioned and they have ticked "Meet standards" for those.

It says:
2 master keys, 1 valet and 2 remotes (if equipped with valet key & OEM remotes, as applicable)

How many keys did you get from the dealer for your elantra or your hyundai car?

 

Exactly that.