The name Danbo is a pun on the Japanese word for corrugated cardboard “danboru”... There’s also a company in Japan that makes cardboard boxes which has Danbooru in its name.
Danbo is a character from a manga called Yotsuba&!, which chronicles the amusing life and adventures of the 5 year old girl the series is named after. Yotsuba&! was first published in August 2003 in Japan. In issue 28 one of Yotsuba’s older friends, a girl named Miura Hayasaka, dresses in a robot costume made from cardboard boxes as part of a school project. Yotsuba discovers her dressed in the costume, so Miura playfully convinces Yotsuba that she is an actual “attack robot”, powered by money inserted into the slot on the chest.
To date there have been four different models of Danbo released by Kaiyodo, the official manufacturer; original, amazon.co.jp, 7-eleven and mini amazon.co.jp. The price of a Danbo ranges depending on size and styple. They can range anywhere from $20 for the mini to $90 for the rare 7-eleven edition.