Around here (Seattle area), Costco is one of the spendier options for tires. Also, they do not know tires or tires sizes, or at least the one near me doesn’t. Hell, I wouldn’t even trust them to check the air in my tires after the last time I checked there while shopping around.
Often times, a dedicated tire store will run similar deals or have such a price difference that buying four at the normal price costs less than three at Costco. However, not all of them can do a full alignment.
I generally avoid dealerships since I have never found a good deal there. I got my tires from a tire dealer and had my alignment done elsewhere. Not quite as convenient, but considerably less expensive.
@john65pennington Precisely right, but how many people even know anything about tires aside from price? Yes, they are round and rubber, but many have a wear rating of 300 or less (they won’t last long), a traction rating of B which makes them dangerous on anything other than smooth, dry asphalt (this includes wet asphalt, any concrete, and pretty much anything else), or have some other defect that makes them an accident waiting to happen. But who cares; they were only $39.95 installed! (Not balanced, just mounted.)