There's much more $ variation in the cruise cost than in the airfare (perhaps for good reason, weather is seasonal and affects cruise enjoyment more). Most of the Sydney people I know who cruise a lot go to USA for cruises as it is "better and cheaper" but of course a different experience. I'd suggest researching the cruise aspect more than air fare, also often you can get discounted air fare as part of a cruise package which will be cheaper than otherwise (esp. for business class).