I can kind of understand people paying for a box that is 20+ years old because few probably survive. $10-$20 is also not that bad. I have paid that or more for backcards and packages if it has been especially rare (like Baby CJ's card, that was around that price I think).
Stuff in stores now seems like more of a fad. And you know, I just had a fun conversation with my first year students yesterday about the advantages of storing money vs food objects. Stored cereal in unopened packages doesn't sound very great to me going forward. Unless the plan is to open it, eat the cereal, keep the box and figure...
In any case, those prices are mad.