Yes, there is a discount off the wine menu if you buy ahead but they are wines that are premium labels and end up about the same price as the non premiums. I think that for example Far Niente Chardonnay was about $50 - 60 onboard and it's $45 at my local Costco.

VOYAGER:
MC to FLL 11/07
MC/Dover 6/06
MARINER:
BCN / Ven 10/11
Alaska 2001|2006
Panama Canal 2003
NAV
Caribbean 11/06
Bermuda|New Eng/Canada 6/04
PG 5/05
OCEANIA
Nautica |Ist/Athens 6/07
Regatta|Baltics 6/08
Riviera 2013 Crossing -Istanbul to Miami