Is it Cheaper to Buy in Bulk?

This weekend I did a price comparison of Costco to Wal-Mart. E and I already know Wal-Mart is cheaper than the other grocery stores in our area, but we weren’t sure about Costco.

E drinks a homemade juice daily, which = a LOT of produce.

 

Reminds me of E on his way to the Jack LaLanne juicer... His chest doesn't look like that ;)

I converted the price to a per unit (or per oz.) cost then multiplied by the # of units or weight of the Costco product. 

Here's what I came up with: 

 P.S. I need help converting Excel to an image to upload here :/

Costco membership is $55/ year, or $4.58/ mo. :)

So will we save money if we shop there at least one a mo. Yes, we saved $8.10 at this one trip alone by getting the big box of Cascade dish washing pods. 

Variables (There's always a rub, right?):

• Will we eat that box of 24 oranges or will they end up in the garbage?

•  The Costco is so crowded and out of the way. We still would need to go to Wal-Mart for other items, so that’s 2 big grocery shops in a weekend. I I get a Wire DVD in the mail (or another show I'm obsessed with) it's doubtful I'll be leaving my nest. 

What do you think- is a Costco (or other warehouse) membership worth it?