The fun thing about the internet is being able to find info on cruises that have already sailed.
In July 2022, the Fantasy had one Eastern Caribbean sailing. It left Port Canaveral on July 9, and stopped in Tortola, Sat. Thomas, and
Castaway Cay.
On July 9, the Norwegian Getaway also departed Port Canaveral. It stopped in Great Stirrup Cay, Amber Cove, and San Juan.
So, while they were both Eastern Caribbean sailings, they were not the same stops.
Unfortunately, we can't price out old cruises. But we can look at 2023 sailings.
The Fantasy 7 night Eastern Caribbean sailing departing from Port Canaveral on July 29, 2023 stops in St. Maarten, San Juan, and Castaway Cay. For a family of four (two adults, two kids), a Deluxe Family Oceanview with Verandah is $10,407.
The Norwegian Escape 7 night Eastern Caribbean departing from Miami in July stops in Puerto Plata, St. Thomas, Tortola, and Great Stirrup Cay. There are a few dates to choose from, with the cheapest date being July 23, 2023. For a travel party of 4, the Haven 2 Bedroom Family Villa with Balcony is $14,364.88 This includes NCL's "Free at Sea" and "2nd Guest Cruises Free". Without the "free" second guest, it would be $27,027.88.
For a Family Balcony on NCL (which is
smaller than the family balcony on Disney) the cheapest departs on July 30, 2023 and is $5,847.88. Without the sale, it would be $9,993.88. So this is where it's actually cheaper than Disney, but only by $413.12.
The absolute
cheapest Haven 2 Bedroom Family Villa with Balcony on the 7 night Eastern Caribbean on NCL for a party of four departing April 23, 2023 is $10,899.88.
Now, let's look at the fees, etc.
For DCL, the fare includes $497.52 in taxes/fees/port expenses. You can add on pre-paid gratuities for $406 for a total of $903.52.
For NCL, the fare includes $1,055.88 in taxes/fees/port expenses, $610.40 in "open" bar gratuities, and $35.60 in specialty dining gratuities for a total of $1701.88. This does
not include gratuities for the dining staff, or stateroom host/staff, which will be $25/person/day for the Haven and Suite level for a total of $700, putting the grand total of taxes/fees/gratuities at $2401.88.