If you only have 1 key, you're going to have to go to the dealer or a locksmith for the second key to be programmed. That may run from $25 to over $100, so pick the dealer wisely by calling around. The reason is, the programming requirement is to have 2 keys working before adding a 3rd or more (up to 8).
Best place to get a transponder key is off Ebay. Shouldn't be more than $15/20 ea.