Different sources quote pricing differently. For instance if you call Disney direct they offer three ways to give you the pricing each time. They ask if you'd like a cabin total, a per person rate or a breakdown? A breakdown gives you the cruise rate, the port charges (also called non-commissionable fare) and the tax seperately for each passenger. The total will come out the same regardless of how they quote it. Be aware that some agencies, for purposes of marketing and getting the phone to ring advertise the lowest possible cruise fare only and don't even include the port charges in the ads. That is widely frowned upon by most in the industry and the more reputable agencies will never practice this marketing approach. Some agencies also have booking fees if you actually want to ask questions or book over the phone with an actual agent. Beware of the fine print and any service that expects you to do an online only booking (simply put in your CC with noone on the phone to direct you and answer your questions or concerns). These type of bookings are often a little lower than through a brick and mortar agency, a full service online agency or booking direct. The reason is, they have less overhead. Less staff and office space required. That little bit of savings may come at a very high price if you need someone to resolve an issue, provide assistance, process a cancellation, change a sailing date etc.
One other point, the cruiselines don't charge a cancellation fee or penalty for having to cancel a cruise outside of penalty period (so many days before your sailing). Some agencies do, again in the fine print. They call it an administrative fee. The simple point is, know who you're dealing with, know what you're getting into by reading the fine print. If in doubt ask about any fees and if port charges are included in the price you're being quoted. The gvt tax will always have to be quoted seperately as it is not included in any of the published rates I know of, even the cruiselines published rates.