Commercial auto insurance cheaper than personal auto insurance?

Generally speaking the answer is NO. Commercial auto insurance is more expensive that personal auto insurance because of the (1) frequency of using the auto- more often in commercial, (2) Commercial auto can cause more damage in accidents, and (3) bigger lawsuits are more evident in accidents involving commercial autos.

There are very few exceptions. For example, a personal auto carried by a 16 year driver living in an urban area with few violations and a certain amount of liability limits can be more expensive than a commercial auto policy for a 35 years old suburban driver, with clean record, for comparable liability limits.