It can come out quite a bit cheaper if you know you'll use it before it goes bad (I buy very little produce in bulk...usually just potatoes and salad veggies because we go through it fast). I buy almost all of my cheese there, a lot of our meats, and a lot of bulk pantry items (such as flour...but we bake homemade bread 3-5 times a week so we go through it fairly quickly). If your area is anything like ours then gas is often quite a bit cheaper at Costco, we've figured that our gas savings will pay for our membership so that's why we decided to go ahead and get the Costco membership as well as the Sam's (our local Sam's doesn't have gas). I'm lucky that we have a small broom closet that's was outfitted with shelves by the last tenant that lived here which I store most of my bulk purchases in, but you'd be surprised where you can find space. My inlaws stored all their bulk purchases under their stairs, my mom had my dad build a set of shelves in her kitchen for bulk purchases, and before moving here I kept it all in a coat closet.
Costco also lets you check out the store before getting a membership (just go up to the membership counter and tell them you're interested in joining but want to look around first). I would also suggest setting a small budget the first time you go in...it's easy to get carried away and spend way more than you think you're spending. I rarely ever spend more than $50 a trip now but when I first started shopping in bulk a $200+ bill wasn't uncommon. Setting a small budget helps you really plan and purchase the things you know you'll actually save on and use.
