Although I don't have a solution for you, I know you won't be happy with the cost. We've seen in this forum members reporting spending anywhere from $300 to $500 for a new fob, programmed to their vehicle.
These things are so expensive and when you get another I believe you need to bring your spare fob in too because they program everything at the same time. You can only have 2 fobs programmed for a car at once and I think all needs to be done at the same time each time you have to replace a lost fob.
please dont create another thread, for the same topic you created 4days ago. its pretty clear (by the lack of feedback) that not many have been in your shoes, or can offer you advice.
i am gonna merge the two threads, and hopefully you resolve you problem and come back to share any new details for others who may cross the same problem.
Not a Santa Fe owner, but in the case of the Sonata, you have to make sure that the Smart Key fob you get is BRAND NEW.
You cannot re-program a fob to another vehicle. The chips inside seem to be one-time use and will only accept one vehicle pairing.
Some sites online swear they can "refurbish" fobs but I would not trust them. You could be stuck with a useless paperweight and no ability to get a refund.
Get it from a trusted source (dealer or online parts house) and try to work out a deal with the dealer who programs it for you. Lowest I have ever heard of is about 300 for fob and programming. And yes you have to have the remaining old fob present or else the programming cannot be done.