It's all about collectability. If there's a pricetag like that on it, then there must be some people willing to pay it. Like adambyte said, that image was not one of the better known ones in the campaign, and it may be available in extremely limited quatities compared to some of the others, hence the price tag. They were handing them out like candy to teacher, and that is one of the ones I've never been able to get ahold of.
One man's junk is another man's gold