Some car keys are not available to aftermarket suppliers and locksmiths but those that are available I invite you to check with me before actually purchasing additional keys anywhere else. I cannot promise you that I will be the least expensive but rarely am I more expensive than most other options. You will have to decide that for your situation.
I originate new keys when all are lost if you have a working key that may not be programmed or I can get the key code from a key code service I use. When I can get them, most codes are about $50.00 and if someone has changed out the locks since it left the manufacturing line it may not work as well. If you push a button to start your car the following would not apply necessarily to you but it could, I can make a metal pattern key for your locks that would do two things; First, it would be flat allowing you to keep it in a wallet to open your door if you lock your keys in your car and second, you would have a working pattern to copy if all keys are lost or stolen. I highly recommend this plan of action even for laser cut keys.
When Subaru went to the Toyota style key blade in 2011 it presented a new obstacle when all keys were lost and the resolution to getting new keys can be very expensive as in $1000 to $1700 for new keys. You might want to do some checking prices before you go ahead with new keys through the dealer, I am usually less expensive and quicker if you twist your key to start your car.