Ah, I'm sorry Sorrel. That's what it looked like on my phone. It looked like the lower ring was curved, which made it look like a WB.
Billy Allens are great, but they are expensive. I would recommend one too except for that OP is wanting something cheap. That would be hard to find cheap even used, since they have a good resell value.
OP, does your horse not work well in a snaffle or something similar? I like french links with rollers, personally, though I've had sucess with full cheek snaffles and such as well. I don't ride in curbs so I can't really give you any advice for those, though.