To replace a key cylinder you need good keys, if they are excessively worn your new cylinder will not work well or will only do so for a short amount of time. The new key cylinder must be coded to the existing key. The costs vary due to key cylinder coding being sublet to keyshops. Replacing the cylinder takes very little time, but up to an hour to code the new cylinder. If you only have worn keys, you will need to get the keycode from a dealer(if you do not have the original key code tag that comes with the vehicle when delivered) then either the dealer or the keyshop will cut you new keys to the code. This is more expensive than making regular duplicate keys. Once you have the cylinder replaced and the new keys in hand, you should have a couple of duplicate keys made of the new keys and change keys once a year if you drive a lot. Key cylinder from dealer is around $80 and expect 1-1.5 hours depending on how well the dealer is equipped. Good luck.