Gourmet Glatt can post their prices online. They can not make a point of posting Season’s prices and comparing it to their own.
Lashon hora is assur even if the listener will figure out the negative implication from information they didn’t specifically hear from the speaker. So, if a price comparison were assur, so would stating one price be assur, because at least some of the listeners already know (or will find out) the other.