An SR-22 isn't a type of car insurance. It's a certificate of financial responsibility that you may be required to file after a moving violation. Your insurer files the SR-22 form to prove you have liability coverage. While the form doesn't raise your rates, the violations requiring an SR-22 can lead to higher premiums.
For New Hampshire drivers, Hanover and Progressive offer the cheapest SR-22 insurance, with annual state minimum coverage premiums averaging $283 and $411, respectively. State Farm and GEICO are the most affordable for non-owner SR-22 insurance, with yearly rates of $326 and $530, respectively.