Royal Caribbean International is branding itself as the "Nation of Why Not," Norwegian Cruise Line cruisers are "Free to Whatever" and Carnival has long been advertised as the "Fun Ship." The challenge for cruise lines now, according to surveys of travel agents, is how to continue building their brands amid a price war. "Price drives them in the door," said Brad Tolkin, president of CruiseOne and Cruises Inc. "They're not saying to their family, 'We've never done a Europe trip before. Let's do it.' They're saying, 'A Europe trip is only $750 per person.' This is uncharted territory."