Speaking as a former travel agent, you can simply go to any travel agent to help you plan your trip. There is no charge for this at all. They have the expertise and will be able to give you the latest bargains, etc.
They make their income from the commission paid to them by the cruise lines. They pass no cost on to their clients. Ask around for a knowledgeable agent and go for it! The cruise companies that say they are the cheapest, are doing nothing more than posting incentives given to them from the cruise lines.
Just so you know, I am a travel agent who exclusively sells cruises and I charge a consultation fee for every booking. I am not a travel seller but an consultant for my client. My client's pay my salary as I work for them and not any supplier.