J. Robert Hunter, the director of insurance for the Consumer Federation of America, an advocacy group, said he wasn’t at all surprised by Mr. Mitchell’s experience. After all, insurers aren’t required to let you know when you’re eligible for a lower rate, and it’s hard to know if you’re getting the best deal (though in California, insurers must sell their lowest-priced policies to those deemed “good drivers,” or people who have been driving for at least three years and have no more than one violation and no serious accidents on their record). “If you shop for insurance, it is quite easy for one insurer to be half the price of another, even in the same group of insurers,” Mr. Hunter said. “It is very difficult to be sure you have the best price,” he added, noting that many agents are working on commission, where higher premiums might translate into more income for the agent.

(Sales people typically collect roughly 8.5 percent of the premium, on average, said Robert Hartwig, president and economist at the Insurance Information Institute, an industry group, but noted that direct-to-consumer companies often spend much more on advertising).

With the exception of New Hampshire, all states require drivers to have liability insurance, which pays for the other driver’s medical expenses, car repairs and other costs when the policyholder is at fault. (Florida requires drivers to buy insurance that covers the occupants in the driver’s car.) The minimum amount you must carry is set by state law, but many drivers choose to buy more coverage to protect their assets in the event of a costly accident.

Still, about 14 percent of drivers went uninsured in 2009, according to the Insurance Research Council, at least in part because some drivers cannot afford the insurance (Mississippi takes the prize for the state with the highest estimated rate of uninsured drivers at 28 percent, while Massachusetts and Maine have rates of only 4.5 percent. New York doesn’t trail too far behind, at 5 percent).

Your insurance rate is probably based on a variety of factors, including your age, gender, marital status, education level, occupation, the type of car you’re driving, where you live and your credit score. Of course, your driving record is also taken into account, as well as how much you drive. (A recent report, co-written by Mr. Hunter of the consumer group, contends that these pricing methods often work against lower-income drivers.)

As you shop around for a new (or better) quote, you should also consider factors beyond price alone, including the insurer’s rating and responsiveness to claims, Mr. Hartwig said. You can typically find that information, including price comparisons and local consumer guides, on your state’s insurance commissioner’s Web site. New York State’s Department of Financial Services, for instance, ranks 40 insurance companies by the number of complaints upheld against them as a percentage of their premium.