As Carlton Bale said, just replace the lock cylinder and key blade.
Here's a short video of how to remove the lock cylinder:
For the immobilzer to work, you need a matching set of 'transponder' from the key fob, 'immobilzer box' under the driver's seat, and 'engine computer' from the trunk. It will not function if you only swap a single component. Best to just keep the set that's already in your car.
Skip to about the 6 minute mark on this video for details on removing the key blade:
https://www.youtube.com/watch?v=Pn16skMu7LI