In Japan, it would be about $5 (Y500) each. And they would taste incredible, because the Japanese learned how to make sponge cake from the Portuguese in the 1500s, and kept making it long after the Portuguese stopped, and then forgot how. In Japan they are called kasutera, which is a Japanization of the Portuguese "castella."
I never knew this before just now. Thanks.
Now I want some sponge cake.
Not easy to make.