We’ve all heard that buying in bulk is cheaper in the long run, but by how much? And if you’re really having a hard time with your bills, is it worth keeping a membership at a big-box store? I have to say both that I’m happy that Costco exists and that I hate having to go there.

While we can get large quantities of the things we use often, we always end up buying more than what’s our shopping list, which increases our grocery bill significantly.

Costco has two different memberships. The first is the Gold Star, which costs $55 and gives you a second card for a spouse or other adult member of your household. The other — the Executive Membership — costs $110 and gives you not only a second card, but two percent cash back on qualified Costco purchases and extra benefits on their other services.

My partner and I also have the Citi Costco Anywhere Visa, which gives us four percent cash back at gas worldwide and at Costco, three percent on restaurant and travel purchases, two percent at Costco, and one percent on everything else.

The Experiment: Amazon Prime vs. Costco (vs. Walmart)

I compared Costco and Amazon Prime, which costs $99 a year for free shipping and access to movies, TV shows, music, Kindle books, and unlimited photo storage. Prime members also have access to Amazon Fresh, which delivers groceries to your door with free shipping if the total bill is $40 or more.

Finally, I wanted to compare Costco and Amazon Prime to the Walmart around the corner from me. You don't need a membership fee, but it’s harder to find organic items if you want that kind of thing.

The Results

Now, we had our first child a few months ago, and families that use disposable diapers know that they’re an expense you can’t skimp on. Buying in bulk would seem to make more sense because we need so many of them. But to my surprise, buying disposable diapers at Costco costs the same as buying them at Walmart. Meanwhile, buying them on Amazon was even cheaper because you save 20 percent on a diaper subscription.

Costco Amazon Prime Walmart
Diapers (Huggies size 3) $0.22 per diaper $0.21 per diaper $0.22 per diaper
Eggs (18 count) $3.59 $1.38 $5.32
One Gallon of Non-Organic Whole Milk $2.89 per gallon $5.84 per gallon $3.98 per gallon
Bread $4.39 for two 100% Whole Grain Kirkland Signature $2.99/loaf for Arnold Whole Grains 100% whole wheat $2.86/loaf for Arnold Whole Grains 100% whole wheat
Toilet Paper (2-ply by Angel Soft) $53.79 for 60 rolls $21.29 for 96 rolls $15.97 for 36 rolls

*Prices were checked on March 29 in the Walmart and Costco stores in Atlanta, GA; and online on March 30 at Walmart, Costco, and Amazon’s respective websites.

While eggs were also cheaper using Amazon, I was surprised by how much more expensive their milk was compared to Costco and Walmart.

So Who Holds the Throne for Toilet Paper — Amazon or Costco?

We compared Amazon vs. Costco to see who had the best value for toilet paper. I thought that Costco would be the best for toilet paper, but the winner on that front was actually Amazon with the Angel Soft brand. That said, if you buy Kirkland, you don't pay much more, since the Kirkland brand costs $23.99 for 30 rolls of 425 sheets each. This comes to $0.02 a square foot, compared to $0.01 per square foot for Angel Soft.

The Pros and Cons of Costco and Amazon Prime

The Costco membership does provide discounts on services like auto care, optical and hearing centers, travel, gas, and pharmacies. Buying prescriptions at Costco without using insurance has been cheaper for us than using a standard pharmacy. At the same time, you get entertainment through Amazon Prime that we wouldn’t be paying for otherwise.

Amazon also provides a wider variety of brands.

I can’t count the number of times I’ve gone to Costco hoping that they’ll have a certain item, only to be disappointed.

Besides, for a family of three, some Costco packages are too big. We can’t make it through the large pack of bananas before some go bad. Even though it may be cheaper to buy them at Costco, if we buy only five at a regular grocery store instead of 12 from Costco, we’re less likely to waste.

I’m also still a little wary of purchasing groceries online. I want to pick my fruits and vegetables myself so that I know whether or not they are good quality. While it may be cheaper to order from Amazon Fresh, that distance between farm and table grows even bigger. At the same time, when I have a shopping list, I may be less likely to buy extraneous items while purchasing online than when I’m strolling down the aisle in Costco or Walmart.

I didn’t compare the price of electronics, which may be cheaper at Costco, but overall, I think I might consider an Amazon Prime membership to reduce my grocery bills!