Can someone please tell me what this is?

According to the manual {in post 7}, A-arms parts #1 and #2 and the given part numbers, they match. You're a good guy Charles S, I don't care what they say about you!

That A-arm could also be fabricated DIY or by a local shop that had a tubing bender, but that seems to be a decent price at the link you provided.
Man, I quit givin' a shit what "they" say or think a long time ago! ;) A shop probably would charge a lot more than that to fabricate them, at least in my area. If I needed them, I wouldn't even consider fabricating them myself, or repairing damaged ones, when they can be bought for $43 each. They could be strengthened easily (a plate fitted/welded inside the "loop", or triagulated tubes, etc.) but that would probably result in worse damage (bent/broken frame) if the kart/buggy were to hit something, probably better to have the easily replaced A-arm get damaged. If Yerf-Dog had just made them more A-shaped/triangular rather than the tubes being parallel, they would have been much stronger.

I just happened to remember seeing that BMI had Yerf-Dog parts so I thought I'd check if they had any A-arms...