Cindy,
I agree with Bob. You definitely need to find out from PADI if they will accept NAUI. The divemasters on the PG are all PADI. I got certified on the PG with people who brought a PADI referral and all they had to do was their dives and the PG divemasters sent in their certification to PADI. As far as cost that changes from year to year, but I believe it is about $350 to 400 as each dive is $80 and I think they will ask you to also do the pool work the first day. Unfortunately calling Radisson probably won't help as all that is determined on the ship. Have fun.