Medigap policies that supplement Medicare’s basic coverage can cost vastly different amounts, depending on the company selling the policy, according to a new study. The findings highlight the importance of shopping around before purchasing a policy.

When you first become eligible for Medicare, you may purchase a Medigap policy from a private insurer to supplement Medicare’s coverage and plug some or virtually all of Medicare’s coverage gaps. You can currently choose one of eight Medigap plans that are identified by letters A, B, D, G, K, L, M, and N (If you were eligible for Medicare before January 1, 2020, but not enrolled, you may also be able to purchase Plans C and F, but those plans are no longer available to people who are newly eligible for Medicare). Each plan package offers a different menu of benefits, allowing purchasers to choose the combination that is right for them.

While federal law requires that insurers must offer the same benefits for each lettered plan–each plan G offered by one insurer must cover the same benefits as plan G offered by another insurer–insurers set their own prices for each plan. This means that the price of each plan varies considerably depending on the insurance company.

The American Association for Medicare Supplement Insurance compared costs of plans in the top 10 metro areas and found huge cost differences. Using the most popular plan–Plan G–for  comparison, the association found that in Dallas the lowest price for a 65-year-old woman to purchase a plan was $99 a month while the highest price was $381 a month. This is a yearly difference of more than $3,000 for the exact same plan.

The association also found that no one company consistently offered the lowest or highest price. In their study, investigators discovered that 13 different companies had either the lowest or highest price. This means you can’t rely on just one company to always have the better price.

When looking for a Medigap policy, make sure to get quotes from several insurance companies. In addition, if you are going through a broker, check with two or more brokers because one broker might not represent every insurer. It can be hard work to shop around, but the price savings can be worth it.