I used to have a similar bread egg everyday. It was very tasty! Japanese mayo, egg, fried. Yum. I forget what I used to pay for that... it probably wasn't much over ¥100 at the time. But this was 20 years ago, so who knows how high that has increased to now. I'd guess around ¥500 if not more.

I have no idea of the history of it or anything else. Just that it was a tasty snack!