Last year, the Candlelight Processional Dinner Packages went on sale in mid-August. They have three price levels (I can't remember how much they were, but we went to Le Celliar last year, and I think it cost about $40). You get an appitizer, your main course, and dessert. The package usually includes 15% off purchases in Epcot the day of the show (we usually save our souviner shopping for the day of the Candlelight Processional to get the discount--usually we save more than the price of the package).
Everytime I've booked a package, I've waited until they announce the narrartors so I can decide which one I would like to see. I think they announced the narrators in October last year. The packages can sell out so I would suggest making reservations before you leave for your trip (you may be able to book while you are there, but dining times and options won't be as good).
Karen