It seems like the easiest way to keep prices updated would be to have an iPhone and Android app (or maybe just a good mobile site) where users or store owners looking to drum up business could add prices for new specials, flag expired specials, etc. Similar to the way Google Maps stays up to date.
Also, does anyone have any insight into just why beer prices are so incredibly variable? It's not uncommon for prices to vary by 50% between nearby stores or even at the same store, depending on the day.