Lorraine, I would urge you to book it with a local travel agent (cruise professional) for a number of reasons.
First, They will make sure you get on the right ship and itinerary that will meet your expectations.
Second, they will get you the best price and then monitor the pricing and get you a better one if the price drops before you cruise.
Third, You will have someone to call when/if something goes wrong and you need some back-up support. This is a HUGE consideration given everything that is going on in the world.
Fourth, A cruise profesional knowledgeable about Hawaii can steer you in the right direction for your comfort level and expectations when it comes to shore activities/excursions.
Just my opinion. Getting the best price on a cruise is an elusive affair. It all depends on when you book, what you book and how it is followed up after booking. Trust me. Use a local travel professional.