A multi-hull vessel almost if not always costs more to build.
Each type of vessel has its good features and its bad features.
Calling the vessel a ‘yacht’ and the fact that you’re talking about sea travel indicates that you’ll be doing a lot of open water sailing.
I’ve designed and built both monohull and cats.
I prefer cats because you get more deck and cabin space for the buck – but, once a cat tips over, you have to do a lot to ‘right’ it. Monohulls are less problematic in many ways, but you can’t beat a good cat. Especially when you stretch a net across the space between the two bows and lay there as the ship goes merrily along (with someone else at the wheel).

I’ve never heard of a “SWATH” yacht. What do the letters stand for?… sounds interesting.

As with just about anything, cost difference probably is a contributing factor, but I haven’t a clue what that really means.