Kerrygold butter is cheaper at Walmart.
Organic chicken stock is cheaper at Whole Foods.
Organic diced tomatoes at Costco however are very well priced.
I have rarely found Costco items more expensive than other local stores, at least for my regular items.
I discount Trader Joe’s since they don’t carry branded items other than wine and beer.
And 2.50/bar at Walmart here
(What I actually buy now is the French cultured butter from trader Joe's though, which is v good)
They carry a variety of branded items including Kerrygold, Tilamook, Rouge et Noir (Bay Area cheese maker), those kringles, Spindrift, Columbus (lunchmeat), those organic herbs, and Tom's of Maine (hygiene). There's probably a few more.
On the bright side, the no-name brand butter is almost as good here, so it's not a total wash.
If you buy Better than Bouillon at Costco, you can get a pound of the stuff for about $6, which is double the quantity that you find at most other grocery stores.
I stopped buying liquid stock after I found that stuff, because it's so much cheaper.
I believe this is a general phenomenon and I read years ago about someone studying it in grocery stores. I'm not sure to what extent it is emergent vs. rationally thought out, but direct competitors tend to evolve to give you just enough good options to get you in the store, and as many bad deals as you are likely to go with just because you are in the store. Being uniformly better is not necessary to compete and therefore suboptimal.
In LA, Costco isn't always the cheapest on a per-unit basis, but they're always the cheapest on a per weight/per ounce basis.
For example, Kerrygold butter is $5 at the Ralphs, and the same size container is $8 at the nearest Whole Foods. It's $16 at Costco...but for 4x the amount of butter, making it cheaper than both Ralphs and Whole Foods if you can actually use all that butter. (There are no nearby Walmarts, and neither of the local Targets or Food4Less' sell Kerrygold.)