I almost never seen a normal product that advertises their retailers margin on it, and/or advertises an alternative cheaper store. Can you imagine walking into a drug store to buy OTC meds and the bottle has a "buy this 30% off online at xyz.com" sticker? No retailer would want that.

I occasionally see MSRP price printed on packaging, which is sometimes mis-matched with the store I'm at - its usually convenience stores and other similar places that add extra markup for high-demand items (and usually you know what to expect).