Generally they are on the standard menu in the Specialty restaurant and sometimes in the Buffet restaurant.
The extra charge items are things like a extra large prime fillet or fillet/lobster combo - I usually do have one of the "specials" per trip as a treat and believe me the small extra charge is more than worth it !
Don't worry you can't accidentally order any of these specialty "extra" items with out you knowing and signing "in advance" for them