School Grade: 3rd (8 years old)
This character combines man ⺅and weapon 弋. It first came to mean substitute from the idea of an army getting stronger as weapons were substituted for man power. When buying things, money is substituted for a commodity; thus 代 also means price. An associated meaning is generation.
(By the way, this description (as well as some others that have already been posted) was literally copied out of this book. I don’t really have original stuff to say about the characters and don’t exactly know how to phrase their origins better than how it’s done in the books that I own.)