I appreciate your investigative tenacity here! I have an idea, and I think I might be on to something. I don’t have a marketing/sales background, but that’s the approach I’m taking here. Here’s my hypothesis. Plain cheerios and honey nut cheerios do not generally compete with one another in the eyes of the company that sells them - the two are bought by different groups. Plain cheerios has its loyal audience. But honey nut cheerios is purchased by people who may purchase one of the many popular sugary breakfast cereals. So the company charges more for plain just because they can, and the honey nut cheerios are priced more competitively to lucky charms and stuff like that to try to sell more boxes.

I’m probably going grocery shopping this weekend and I’m curious to check the prices out. I’m a toast person :P