Royal Caribbean usually charges 150% whereas most everyone else charges double for cruising solo. NCL has some single cabins on the Epic and their new ship. Carnival used to have a catagory for singles, but I believe they've done away with it. My suggestion is to select the itinerary you want, then find out who cruises that itinerary, then price it out. A good travel agent certified in cruises (CLIA) would be a very valuable asset.
I've cruise many times solo and enjoyed every single one of them! You can do what you want, when you want, without having to worry about anyone else's schedule. Please let us know what you select. Curacao is a great little island to visit, very colorful!