Warehouse clubs have thrived during the recession, as cash-strapped shoppers look to score sizable savings over the local supermarket and even discount stores. But that doesn't mean you always get the best deal at the warehouse club.

We checked prices at a Chicago Costco store, then priced those same items at nearby supermarkets, drugstores, discount stores, and online retailers to determine if the membership club always offered the best price. We found more than a few bad buys. Here are the six items that you shouldn't buy at a warehouse club:

Milk
This most basic family staple is a regular in most grocery stores' weekly advertisements, and for good reason. Shoppers typically buy this weekly, and now that discount stores carry dairy products at low prices, it's imperative that grocers have the lowest price on this staple. We priced a single gallon of whole milk.

Safeway-owned Dominick's: $1.99 a gallon
Costco: $2.10 a gallon

Diapers
If you think household staples like baby diapers are cheaper to buy in bulk, think again. Mass merchants like Walmart and Target regularly offer diapers at a deep discount, since it's one item that will keep shoppers returning to the store. You may not beat the Costco price, but you'll come awfully close. Walmart tied the club store in price and while local supermarkets typically charge more, readily available coupons (we found $2 off on Huggies, the same brand we priced at all the stores) will lower the per unit price below that of the membership club.

Costco: 22 cents per unit
Walmart.com: 22 cents per unit
Albertson's owned Jewel-Osco: 27 cents per unit
Walgreen's: 35 cents per unit

DVDs
When it comes to DVDs, you can shave a dollar or two off a club store price by shopping discount stores and Amazon.com. Promotions are fierce with popular titles, but it's a lot harder to get deals after the initial promotional period. Retailers run hot new releases as loss leaders, forgoing profits and risking their relationships with movie studios that are reluctant to devalue their product. Older titles are usually better buys at club stores once the shine has worn off the discs.
We priced The Twilight Saga: Full Moon DVD, 2-Disc Special Edition.

Walmart.com: $17.00
Amazon.com: $17.49
Costco price: $19.99
Bestbuy.com: $24.99

Toilet paper

It's a common misperception that paper products are always cheaper in bulk. But even your local supermarket can beat the warehouse club if you take advantage of coupons, specials and loyalty club programs. Not always, mind you -- one local grocer came in a bit more expensive than the membership club without a coupon.

Jewel-Osco: 53 cents per roll
Kmart: 56 cents per roll
Costco: 65 cents per roll
Dominick's: 67 cents per roll

Holiday promotions

All bets are off when it comes to holiday promotions. This is when supermarkets often have surprisingly low prices. Memorial Day, Fourth of July, Labor Day, the Super Bowl -- if there's eating planned, grocery stores will run eye-popping deals on all the staples. Check the ads and in-store promotions carefully before shopping. While membership clubs can present a great everyday value if you buy in bulk, grocers will pull out all the stops for special occasions.

Non-bulk items

There's one hard and fast rule when it comes to the value found at membership clubs: If the amount is more than you can use or comfortably store, it's not a bargain. Buying in bulk can offer huge cost savings, but only if you actually use it.

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