A few days ago, I was muttering on @Shel_B's How big is an onion? topic about only being able to find bowling ball sized onions. Someone in my local supermarket must have read that. Today, they were stocking these. Mini red onions (the default type here).
I have had them before, but not regularly. I use them like shallots.
¥11.98 / $1.65 USD per kg.