This is also my experience. Recent example, I can buy a 1.9L container of mayonnaise for $8.99 at Costco to make homemade potato salad for my grandmother’s 95th birthday party. But I forgot to prepare until the last minute and realized I had no mayo, and so I went to the local place who charged $7.99 for 443mL of mayonnaise from the same brand.
Amazon sells 3.78L of mayonnaise (dear God who needs that much mayo?) for $18.70, making them not quite as competitive as Costco in terms of price per mL, but pretty damn close, and moreover still way better than the local place.