How do you estimate commercial insurance rate for a property?

[Gina Schulz]

I'm putting together a proposal for a potential buyer of an investment property.  I'd like to include an estimated insurance rate so the numbers I present are at least close to what reality would be.  Insurance brokers can't put together an estimate without disclosing tons of info.

Is there a "formula" one could plug some numbers into to come up with a realistic estimation?