How do I estimate insurance costs?

[Robert Muzyka]

How do you estimate insurance costs when your analyze a potential rental deal?  I am beginning to analyze deals daily (and in different markets around the country) and I'm not sure how to come up with a good estimate for monthly or annual insurance costs?  Any rule of thumbs that I should know about or websites/resources to utilize to come up with a rough estimate for my initial analysis? 

Thanks!