Not paying attention to where you're buying your prescription drugs could cost you—to the tune of $100, or more, says a Consumer Reports analysis.

Secret shoppers posing as uninsured consumers called 200 pharmacies nationwide in order to uncover the cost of a month's supply of each of five popular prescriptions that went generic: Lipitor, Plavix, Lexapro, Singulair, and Actos.

Costco proved to be the most cost-effective for consumers overall. On the other end of the spectrum, shoppers who went to CVS risked paying up to five times more for some prescriptions.

Why such a huge price difference for the exact same bottle of pills?

It all depends on how important the pharmacy is to a store's overarching business model, Lisa Gill, a prescription drug editor for Consumer Reports explained in a company press release.

For example, a big-box wholesaler who boasts a wide product offering that ranges from chicken breasts to flat-screen TVs is likely aiming to entice consumers with their low-cost pharmacy, with the hopes that they will purchase other items.

Given that many of these men and women take at least half a dozen different prescriptions to help them manage everything from heart disease to diabetes, finding ways to keep medication costs down is vitally important for seniors and their caregivers.

Browse Our Free Senior Care Guides

Medicare will help cover the cost of an older adult's prescription medications, but the program won't pay for everything. (Learn what is and is not covered by Medicare, as well as the pros and cons of Medicare coverage)

Once you factor in monthly premiums, the plan's deductible and the various co-payments involved, the cost of prescription medications can quickly add up.

Consumer Reports offers a few strategies for taming medication costs:

  • Opt for generics: Generics can be an extremely cost-effective alternative to brand-name drugs, if a senior can tolerate them. The patents preventing many popular senior medications from being able to be produced generically have recently expired. Talk to your loved one's doctor to see whether any of their prescriptions can be swapped for generics.
  • Buy in bulk: People taking long-term medications (i.e. Lipitor to manage high cholesterol) may be able to reduce their costs by buying a 90-day supply versus a 30-day supply. Most retailers offer discounts for those who can purchase pills in bulk.
  • Ask for a lower price: Many of Consumer Reports' secret shoppers weren't provided with the lowest price for a particular drug right away, they had to dig a bit deeper and inquire about discounts and special offers before they hit upon the best price. Don't be afraid to negotiate and try to unearth the best price for a given medication. According to Gill, "A consumer can't assume that the price of their prescription medications is set in stone. One of the big takeaways is that you have to ask for coupons or inquire as to the best price and see if your pharmacist will work with you."
  • Don't shun mom and pop drug stores: People assume that chain retailers automatically present the most cost-effective options when it comes to most items, including prescription medications, but Gill says this isn't always the case. Independent pharmacies have an incentive to maintain a solid relationship with their customers, she says. Thus, they are more likely to help their regulars get the optimum price for their prescriptions.

Discover more money-saving tips and print out a pharmacy comparison checklist: How to Find Low Cost Prescription Drugs