Here's Why Costco's Monthly Deal Book Isn't Always So Helpful

Costco is known for its fabulous prices on bulk grocery and household items. And joining Costco can be a smart personal finance move because the fee you shell out for a membership can more than make up for itself in the form of savings during the year.

But sometimes, Costco manages to outdo itself price-wise by discounting certain items. Usually, Costco puts different products on sale every three to four weeks. And it informs its members of those sales via a monthly mailer -- a deal book of sorts.

I happen to find that mailer less than helpful, though. Here's why.

When you don't get the full picture

There are certain items I buy at Costco all the time regardless of price. For example, I've found that Costco has the best prices on milk and egg in town. So if we need to stock up on those items, I'm buying them even if they aren't on sale.

But then there are those items I'll try to only buy at a low price because I'm not sure how much I'll like them. The problem with Costco's deal book, though, is that it only shows you how much money off you're getting for a given item; it doesn't tell you the final cost of that item. As such, it's hard to use the deal book to create a grocery budget for the week.

Of course, there's a reason for this. Costco's in-store prices vary from one market to another. So it's easier for Costco to blast out a deal book to all of its members, regardless of location, highlighting the discounts it's offering. It would be more cumbersome and costly for Costco to send customized mailers to members based on their geographic location.

But for example, right now, Costco has Girl Scouts Thin Mints Bites available at a discount. If you look at the mailer, which is also accessible online, you'll see that they're $3.60 off.

Based on my love of the original Thin Mint cookie, I can't imagine this being a product I won't enjoy. But without knowing the final price, I'm not sure I'll plan to add it to my shopping cart. Since it's an item I'm not familiar with, for all I know, even with the $3.60 discount, I could be looking at paying $9, or $12, or $17.

I'd probably be willing to take a chance on a new snack at the lower end of that range. But I'm not sure I'd pay much more than $12 in case the flavor isn't to my liking.

How to get a better sense of what Costco products will cost in stores

The easiest way to figure out what Costco is charging for various items is to walk into the store and look at price tags. But if you're someone (like me) who tends to fall victim to impulse buys, you may prefer to bring just enough cash with you to do your food shopping to avoid that temptation, rather than using your credit card. And it's hard to do that when Costco doesn't publish in-store prices in its monthly deal books.

One option is to call your local store and ask for a price ahead of your visit. Another thing you could do is check out the online price for the item you're interested in. Usually, in-store prices are cheaper, so you can see what the online cost is and subtract 10% to 20% in your head, which is probably in the range of the difference you'll be looking at.

That only works when Costco sells the item you want online, though. In the case of those Thin Mints Bites, apparently they're in-store only, so my only option for figuring out the price ahead of time is to call my local store.

And to be honest, because I know how busy it tends to be, I'm not going to do that. I can wait until I hit the store to check out the price for myself.

All told, Costco's deal book can be useful in that it can alert you to when items you buy regularly are going on sale. It's just less helpful when you're interested in new items but want to know their cost.