I don't know what data they base their risk on but it sure seems to me that someone is either trying to make a lot of money or they don't have a good idea of what their risks are.  The bottom line is that if you are a NRA member you can buy insurance to cover lawyer and liabilty costs if you use your firearm in self defense.  For a $100K benefit it cost $165/year and for a $250K benefit it costs $254/year.