jim, how'd you make those pickled onions when we were at the coast here?
1/2 cup red wine vinegar
But the ratio depends a bit on what the r.w. vinegar tastes like and what you want the final product to taste like. Use less salt if you want them to be mostly sweet, or obviously more salt if you want them to be kind of salty. Not sure what the olive oil is doing in this equation, but I read something once that used it so I do. Could probably experiment without it. Also, you could just use sugar instead of the honey.
For a lot of other bases (fennel, cucumbers, etc....) I prefer rice wine vinegar or apple cider vinegar. But for some reason I use red wine vinegar for the onions (I guess because I've been making it.)