There are quite a few so-called "tactical knives" on the market. Many of these knives have handles large enough to extend below the hand, exposing the butt. Any of these are likely strong enough to use as an impact weapon if needed.
I often carry a Spyderco Police with the all steel frame. It has a large handle, and the all steel construction gives it a bit of heft. It would certainly get someone's attention if I had to hit them with it. It will also break auto glass if necessary. It's a bit more than $100, but there are lots of other choices.
Andy