You have to mix the flour with a little water, though.
I found a 1.87 lb. bag for $8.99 at a Japanese-Korean grocery that's just a 15-minute walk from my place.
If that fills a 1-quart measuring cup (it likely does), that would be the equivalent of 64 eggs.
So the cost of a dozen "eggs" would be...$1.68. But I suspect the bag holds more than four cups worth, so the price would be even lower.
I'll have to keep it in the freezer after I open it, since there's no way I'm going to be baking enough times per week. But it's good to know I can buy fewer eggs in general.
Interestingly, it was the last bag on the shelf. That probably indicates how slowly it sells; other flours, such as rice flour, were well stocked. (Also, the clerk didn't seem to be familiar with the product at first, when she was searching the baking shelves. Her supervisor then found it. It only says "soybean flour" in English on the BACK of the bag, which is why I didn't spot it on my own.)
There were smaller bags of soybean POWDER next to it, but the price was just over $7 a pound. Clearly not worth bothering with.