Thanks, everyone, for the suggestions.
The straight-edge with a deckle pattern may be the way to go. I'm also thinking I could take a "blank" straight-edge and grind the exact deckle pattern I have on some vintage photos. That shouldn't be too hard.
And if that doesn't give me the look I'm after, I'll reconsider the Fiskar shears, or the rotary cutters from the craft stores.