Twins are definitely worth looking at. Those that have actually owned them can tell you they don't cost that much more to own and fly than a heavy single. I've written somewhat extensively on the topic here.
I could get my Seneca III to run LOP. Most Seneca IIs can't. I burned 18-19 GPH total for 165 KTAS in the 10,000 ft range. And that cabin is absolutely HUGE, a full 7" wider than most light twins. The back door and club seating are very nice for families with small children.
Singles can lead to outrageous annuals too, that's not limited to twins.
I bought my first twin after owning a Bravo. My Bravo burned 19.4 GPH in cruise (most Bravos don't run LOP well, mine didn't). I figured if I was going to burn about 20 GPH, I wanted a second engine.
Comparing my previous Bravo to my current Baron: The annual on my Baron is very close to what the annuals ran on my Bravo so no noticeable increased expense there. The hangar's the same, insurance is less on the Baron due to a lower hull value. The Baron climbs faster but the Bravo cruises faster (on similar fuel flows). I also fly the Baron at a lower altitude than I did the Bravo since the Bravo required higher flights for better efficiency. And then I was wearing oxygen regularly. A typical trip has very little difference in total time or fuel burn. And you can overhaul two IO-470 engines for about the price of one TSIO-540. It just doesn't cost that much more to fly a Baron than a Bravo.
But, I have over 1700 lb useful load, six seats and nose baggage (and did I mention air conditioning) in the Baron that the Bravo doesn't have. And the Baron actually climbs in most flight profiles after losing an engine. The Bravo, not so much