you guys would be surprised at how easy it is to make a typo like that. As someone who oversees our (the company i work for) email campaigns you get a sense for how easy it is to screw up. You can have anywhere from 1-4 people involved in setting up a single email campaign.
The guy creating the promotions, doesn't actually create the graphics.
The graphic guy accidentally copy/pastes the wrong price and doesn't even realize it, then sends it off to someone to test and verify everything is correct, but that person is busy doing something else or just thinks the guy who creates the deals and promotions is throwing a really epic promotion and signs off on it and before you know it the entire world (or email list) see's it.