The cruises that port in Colon have cheaper port fees and taxes. The carnival ship does not go into the canal. You have to book an excursion on a smaller boat that will take you into the canal.
The cruises that specify partial and full transit actually have the carnival ship go into the canal and through the locks. The port fees and taxes will be higher for these options.
In the past when I priced out the different options, the price was a wash. Whatever you save in fees and taxes by going to Colon, you end up spending on an excursion. It’s a matter of whether you want a view from the ship or the view from a smaller vessel.
When I look at January 2024 Panama cruises, I see two listed with partial transits, and one listed as Colon (no transit).