Costco and Amazon don't always list the exact same products. Costco carried a 140-count pack of 13 gallon trash bags for $18.99, and Amazon carried an 80-count for $15.54. For a few dollars more, you can get double the amount at Costco.
Beauty products also were generally less expensive at Amazon. A two-pack of Aveeno lotion was $15.49 at Costco, but buying two single bottles of the same product on Amazon totals $14.38.
Costco sells a 180-count pack of its Kirkland brand makeup wipes for $15.99. On Amazon, a 50-count pack of Neutrogena brand wipes is $8.89. Costco offered a better deal in this case.
Groceries were generally cheaper at Costco. At Costco, Starbucks 60 Pike Place Coffee K-Cups cost $36.99. At Amazon, the exact same product cost $42.71.
Amazon sells a few of Costco's private label Kirkland products, but they are more expensive at Amazon. An 84oz. jar of coconut oil was almost half the price at Costco compared to Amazon.
After comparing prices across a few categories including cleaning supplies, beauty products, and groceries, Amazon had lower prices on most cleaning and home products.
But Costco had better deals on bulk quantities, and the groceries and Kirkland-brand products were significantly cheaper at Costco than on Amazon. It didn't have as big of a variety in terms of brands, but Costco had lower prices a majority of the time. A Costco membership is also much cheaper than a Prime membership, making Costco the winner here.