Have the range owner call the NRA they have range operators insurance programs. My club buys their insurance from the NRA approved/endorsed provider.
Insurers are businesses like any other.
In the consumer end of the market, the rates are highly regulated, and must be filed and approved by the insurance commissioner of the state where the policy is issued, this rate must be backed up by an actuarial study of the actual loss experience for the line of business involved.
State regulators will not allow a gross underwriting profit in any state I have ever been involved with.
Commercial lines of business which would include the liabaility on a firing range, are less regulated, but if the company is admitted they still must file a rate plan based on experience and get it approved.
Competition between companies usually keeps rates under control as well, but not many companies write range operators liability. The bottom line is shop around rates can vary widely by carrier.
ISO = Insurance Services Office, an association of Insurers, not a government agency, for a fee ISO provides approved policy forms, and rate filing plans to member companies. ISO was founded to help cut the costs of filing rate plans and forms in 50 different states. Members use what ISO has developed to avoid having their own staff to do this, it lowers the cost of operations for member companies.
Call the NRA for all your firearms related insurance.