Quote from @Katherine Serrell:
Not a dumb question! In my opinion, the best way is to just call a local broker. Insurance depends on so much including the specific property. The state/city, type of property, age of the home, location, cost to rebuild, flood zone, age of roof or major systems, your deductible, etc. all factor in. I would identify the area or a few areas you are looking to invest and just call 2-3 companies and give them an example property to get a ballpark idea. The biggest, most common factor that I can think of that can really drive up the cost is if the property is in a flood zone which you should avoid anyway.
Just a tip, when practicing analyzing the numbers, if the math is so tight that the insurance being a bit higher than anticipated is what makes or breaks the deal then that is probably a good indicator that it is not a good deal in general.
What Katherine said! Not a dumb question, but it's so granular there are no accurate "ballpark numbers."
Agents don't consider it "wasting their time" if you will use them when the financials are lined up. We're all human and things take time.