The model of Mercedes or BMW that you own will be a determining factor in the actual cost difference between the two cars, including the amount you will pay for insurance. In general, a Mercedes will be quite a bit more expensive, although the total cost of insurance is a couple thousand dollars lower. For the comparison used here, popular 2-door versions of both cars were used.
Over a 5 year period, you can expect to pay around $2,378 per year, and a total 5 year cost of around $11,905. By comparison, the BMW will cost about $2,631 per year, and over $13,100 for the 5 year insurance cost. If the cost of insurance is your primary consideration, the Mercedes will be the lower cost vehicle, although the BMW has a lower total cost of ownership.
One reason the BMW has a high insurance cost is because the Mercedes is recognized as a world leader in vehicle safety innovation. By making their cars safer, the company reduces the risk of insuring it, and that reduction is passed on to consumer in the form of lower annual insurance costs. This is not to say the BMW is more dangerous to own, only that it may not have the same level of advanced safety enhancements that a Mercedes is known for.
Another factor to consider is your actual cost of insurance. Since the sample costs are based on a driver with both excellent credit and a blemish-free driving record, your actual rates may differ considerably. Other factors that can cause you to pay higher rates are your marital status, where you live and where the car is parked at night, and even how far you expect to drive the car each year. All of these factors must be considered to get your actual cost, and the costs given here are used for base comparisons only.