Insurance is based on a numbers game of statistics and data that the policy underwriters consider when assigning rate classifications. Cars that tend to get in more accidents, or require more expensive or more thorough repair than other cars will have a higher claim rate and thereby a higher premium to insure these higher risk vehicles. Using this information backwards you can find the lowest end of the scale. There are some vehicles that are so cheap to insure they are practically free.
Some obvious deductive logic can help you to identify the high risk car category relatively easily. Sports cars, big engines, expensive repairs like luxury cars or some imports are all likely to have high insurance rates.
A 2002 Honda Civic or Mazda is going to have a higher rating than a 2002 Hyundai Accent. In addition to the Accent being more modest and slower than the other cars, the occurrence of accidents with Accents is likely substantially lower than the occurrence of crashes with a Honda. This is specifically due to the subculture movement of sport economy cars making it fashionable to take certain cars and modify them heavily and in many cases drive them recklessly. The difference in these insurance rates can amount to easily more than $100 per month that you could be saving.
Insurance companies tend to regard 2 door vehicles as increased risk as well as new vehicles which are more expensive to repair than older vehicles. Looking for a four door car will almost certainly save you money on insurance premiums regardless of what you buy. Try to choose a vehicle that might be associated with good drivers or perhaps a car that has an especially low accident repair occurrence.
A good example of this would be larger trucks. One might think that a larger truck has a big engine so it will be expensive to insure. This can be true for some trucks, especially sport trucks, but another factor is at work in the equation.
Since a large truck colliding with a Honda Civic might not even require a paint job, but the smaller car will be massively damaged even from a minor collision, some trucks and vans can be incredibly cheap on insurance. It is important to note that the larger vehicles require substantially more fuel than an economy car so this must also be considered.
Doing online quotes for insurance will make it easy to find which vehicles are the lowest cost. Then it is simply a matter of locating, inspecting and purchasing that make, model and year of car.