For true frugalistas, Costco is a way of life. This membership-only warehouse club is the largest in America, and the second largest retailer in the world behind Walmart. Chances are, you or someone you know is a member.

But despite its reputation as one of the most budget-friendly retailers around, many Costco customers misunderstand just where that value can be found — and end up overspending as a result. Like any successful bargain business, Costco makes its profit on the least-savvy shoppers in the store.

Finding significant savings at Costco requires a little planning, a lot of know-how, and a bulk-sized amount of self-control. Here’s a road map for your next trip.

Photo: Thinkstock

Check Out the Pharmacy and Optometrist Counters

One of Costco’s best deals isn’t in the meat or produce aisle — it’s at the front of the store. The Costco pharmacy is a national treasure, with prices significantly lower than name-brand drugstores. A study from Consumer Reports found that Costco had better deals than CVS and Rite Aid, sometimes by more than $100.

People who have to pay for their prescriptions out of pocket will especially benefit, since most pharmacies price their drugs based on what the insurance company can afford. Costco members are also eligible to enroll in their pharmacy savings program for free, as long as they don’t have prescription coverage from their insurance provider.

Costco optometrists also generally charge less for exams than other doctors. Their frames and lenses are also usually cheaper than what you’d pay at your local eye doctor.

Photo: Thinkstock

Apply for Rebates

Many Costco deals look great because they come with a post-purchase rebate. But to score the extra discount, you have to remember to send in the rebate and receipt. If you don’t, you’ll end up losing out on potential savings.

Set a reminder in your phone to send in the rebate. All it usually requires is filling out a short form, providing proof of purchase, and mailing it in. Make copies of your receipt in case it gets lost and mark on your calendar when you should receive the rebate by.

Stock Up on Discounted Gift Cards

Most grocery stores sell retail gift cards, but Costco is one of the few that sells discounted gift cards. A quick scan of their website shows an AMC four-pack deal for $35.99. Ticket prices vary based on your location, but tickets for an evening showing in New York City cost $14.99. Even in Little Rock, Ark., the average price is $10.99. No matter where you live, finding movie tickets for $7 apiece is a bargain.

Restaurant gift cards are also popular at Costco, which sells two $50 gift cards to McCormick & Schmick's seafood restaurant for $79.99 — more than 20% off. If you’ve already planned an evening out, check if Costco has gift cards for the venue or restaurant of your choice.

Know What Deals You’re Looking For

Costco has a reputation for being a high-quality and low-price retailer, mostly because you can find a better stock of items without paying higher prices. Unfortunately, customers who only care about finding the best deals might struggle at Costco.

Don’t assume Costco always has the best prices on everything. You might find that their canned tuna is cheaper than what you’d pay at your regular grocery store, but that their ground beef is more expensive.

Look at what you typically pay for your staples and compare that to the prices you see at Costco. Create a list of which products are cheaper at Costco, and only make the trip when you need those items.

Save on Printer Ink in Their Photo Center

One of Costco’s best deals is entirely hidden in their photo center. Costco offers refills of printer cartridge for $10 or less. Customers bring in their empty used cartridges and wait to get them filled. Not only is this more environmentally friendly, it’s also much cheaper than buying a brand new cartridge. Plus, independent articles reveal that Costco’s ink quality is almost as good as the manufacturer’s, while more than half the price.

While you’re there, you can order photos and other prints. Costco’s prices are slightly cheaper than Shutterfly, one of the top online photo retailers.

Skip Prepared Foods

Costco is famous for their premade snacks, like pigs in a blanket and cream puffs. But unless you’re hosting a party, there’s no need to stock up on wontons and assorted cheesecake bites. These items are budget-killers for anyone trying to eat on the cheap.

A key rule for cheap grocery shopping is to buy food that’s as far from being ready to eat as possible. A whole chicken will always be cheaper than chicken breasts, and frozen chicken breasts will always be less expensive than microwave-ready lemon-marinated chicken. Of course, this presupposes that you’re willing to do a little cooking.

Only Buy as Much as You Can Eat

One of the easiest ways to overspend at Costco is to let your purchases spoil. Costco’s bulk sizing can make it difficult for a single person or a couple to go through all the food at once. Even though that tub of hummus might be cheaper per ounce at Costco than at your local grocery store, it’s still a waste if you can only eat half before it goes bad.

Before you leave the house, go through your pantry to see what you already have and what you need. That will keep you from buying another case of diced tomatoes when you already have five cans in the pantry. If you notice that you never get through the Costco-sized mayo or relish, don’t buy those items next time.

Magnify Money is a price comparison and financial education website, founded by former bankers who use their knowledge of how the system works to help you save money.