When you buy a new car there are many important budget considerations in addition to vehicle price: How much gas will it drink up? Will it need repairs in five years?

Car insurance premiums can add substantially to the annual cost of operating your auto. But how much do you research a vehicle's potential insurance costs before you sign the paperwork and drive away?

"There isn't a real insurance consideration made in the sale," says Tom Hoffman, president of Leo Hoffman Chevrolet in City of Industry, Calif., a dealer of Chevy Silverados, one of the most expensive to insure on the list.

Car dealers nationwide agree that insurance is a secondary consideration among car buyers: All estimate that less than 10 percent, and sometimes less than 5 percent, of their customers research a vehicle's insurance costs before buying it. The only exception is on specialty vehicles, like Corvettes, when buyers become more aware of a potentially large insurance bill, says Richard Llewellyn of Palm Automotive Group in Punta Gorda, Fla.

Insure.com has calculated the most and least expensive autos to insure among the nation's 20 best-selling vehicles.

If you happen to own one of the above autos, your auto insurance premium will be different — possibly considerably different, depending on how your personal rating factors (driving record, town and credit history among them) differ from the situation used to calculate average premiums for each vehicle.

Why premiums are high for these vehicles

Your own premiums are calculated using sophisticated tables combining your personal factors plus the "loss experience" of the vehicles. That means that you could be the best driver in the world, but if other drivers of your car model are regularly crashing their cars, that car is going to be more expensive to insure.

Insurance loss histories compiled by industry groups and insurers are used to judge the level of claims a vehicle will incur for collision damage, medical bills, theft and other factors. The chart below shows exactly where these vehicles have higher-than-average insurance losses (where available).

I have to have it

These vehicles are among the top 20 best-selling list for numerous reasons, none of them insurance related. Corky Pace of Haddad Dodge in Bakersfield, Calif., who estimates that 5 percent of his customers consider insurance premiums, says that the motivating factor is "you have to have it, or you want it." Pace, who sells Dodge Rams, also observes that "the truck is the new station wagon," used to haul around work gear on weekdays and the family on weekends.

Hoffman says that styling and ride are the ultimate deciding factors for Silverado buyers. He says the Silverado's interior, trim, upholstery and seats "make them feel like they're riding in a passenger car."

The hybrid engine is the motivating factor for Prius buyers. Llewellyn, whose dealerships include Toyota, says that the Prius's "perceived gas mileage" attracts buyers. He notes that the Prius's gas savings kick in if you don't drive more than 30 to 50 mph; but if you live in a state with a lot of highways, your gas mileage will be only average. "It depends how you will use the vehicle to capture the savings," advises Llewellyn. In addition, because the Prius is smaller and lighter than many other vehicles on the road, "you can get run over easily," says Llewellyn.

Methodology

Insure.com's list is based on the 20 best-selling autos in the United States according to Reuters News Service as of May 2007.

In order to develop the insurance premium for each of the autos, we assumed a single male driver, age 40, who owns his own home, has a bachelor’s degree and no accidents or driving convictions. The insured works as an administrator in a hospital and drives 5 miles to work one way.

The policy limits for our imaginary driver were $100,000 per person and $300,000 per accident for bodily injury and $50,000 for property damage. Minimum Personal Injury Protection (No-Fault) was included where applicable. The policy has a $500 deductible for comprehensive and collision losses.

Insurance premiums were developed for three different cities, one on each coast and one in the Midwest. Quotes were obtained from four different insurance companies in each city. The insurance cost for each auto was then averaged across all three cities and all insurance companies.