On the DDP the Fantasmic package costs 1 TS credit per person for Mama Melrose or Hollywood & Vine, and two TS credits per person for Brown Derby. And yes, you get an appetizer, even on the basic plan (only with the package reservation).
You must call 407-WDW-DINE to reserve and ask specifically for the Fantasmic package. You can't make the reservation online, and it's not the same as a regular reservation.