Have you priced used cats? Cats hold a better market value than monos. That's a fact. Also, the price of new boats keeps going up, so the used market tends to rise with it. I could sell my tri for more than I paid 4 years ago (and when I bought mine I was in a bidding war against another buyer). I sold my prior two tris for more than I paid each time.

The purchase price for multihulls might be higher but the Total Cost of Ownership (TCO) is lower, in my limited experience.