Insurance In Helena Montana
Insurance went from $900 t0 $5500 per year.
5000SF office space and a 1000 SF living quarters in a primarily residential neighborhood.
The living quarters kitchen and the office building have a shared wall where they adjoin.
Any ideas? I am sure that there is cheaper insurance out there somewhere. The current insurance company is moving out of state. 
Stockpro,
I'd find a local (Helena) REI group and look for Agent referrals...how about your Agent???
From retired insurance broker. $900 to $5,000 a year??? Something is terribly wrong unless there has been a substantial change in the character of the risk (building). A new tenant doing something that an insuror considers high risk could cause the problem. Any change there?
Call your state fire rating bureau and get the fire rate on the building. See if that has changed for some reason.
Then start shopping the risk to a several insurance agents. Call a few "captive agents" like Nationwide and State Farm. Also call a few Independent Agents that have contracts with several different insurance companies. If by some chance Erie Insuance Exchange is licensed in your state get a quote from them - very competitive company.
The agent who is representing you should have shopped the insurance before he laid the increase on you. Sadly, 90% of insurance do not give the service to clients that they should. They only care about collecting the highest commission they think they can get away with. NEVER fall in love with ANY insurance agent. Start shopping every year about 90 days before policy expiration.
Was given notice that the current company is no longer doing business in MT and that new insurance was needed. Contacted many agents but all were expensive because of the joint residential/business use of the property and on stated because the residence kitchen and the office building share a common wall.
What is the wall structure? Going to assume it's 2x4 studs with dry wall finish.
Possible options. Turn the 1k living quarters into commercial space -no kitchen. Get an estimate to build a firebreak wall - cinder block with fire rated drywall.
Still suggest you check the fire rating on the building.
Have to wonder how far away is a fire dept. Is it paid or volunteer?
How far nearest fire hydrant?
One more option. Get an agent who knows what he is doing. Say the building is worth, just to easy numbers, 100K Get a quote on a named perils policy for 20k. Have the agent shop the other 80k telling the other company(s) that you want a 20k deductible. this is often called "layering" policies. No one company is willing to take on the entire risk so you spread the risk over two or more companies.
Be sure to tell the agent to quote "concurrent" policies..That is to say the lanquage of each policy will read essential the same without conflicting clauses.
I would bet if you can find a broker, not an agent who deal with Lloyds of London, they would offer a reasonalbe rate if you have underlying policy in place. You would in effect tell them that you want the 10 or 20k deductible.
I've done this layering tactic for many clients when I was in the biz.
Good Luck!
P.S. I'm getting the impress you are coming up agents who are lazy.