No, not the waitress at the truck stop, but the print on demand store where many OSR products are sold.
HC50 gives you 50% off hardcovers, and FLASH30 gives you 30% off softcovers.
50% is about as good as it gets, actually. Usually they have a 40% off sale in December. But if you want a hard cover, now is the time.
Ends midnight on the 24th of November.