Find a locksmith based on the link below, type in your zip code for a list of reputable ones in your area. Some good automotive locksmiths can do these keys for our cars. Generally, for cheaper than a dealer. However, based on what i've read on here, average key cost is around $250-350.
Speaking as an automotive locksmith myself, we won't be MUCH cheaper than that price based on our cost for these keys.
http://www.findalocksmith.com/search.aspx