Regarding cost: it depends upon the zone and how high your home is raised above the ground. It can range anywhere from a few hundred dollars per year to several thousand. It doesn't matter who you buy the coverage from, the rate is the same, being set by the government. My own home is in an 'A' zone and I pay about $425 per year, but it's raised about 3 feet above ground level. The flood elevation (set by FEMA) for my lot is 1 foot above ground level. That means my home would need to be raised at least 1 foot to get flood insurance. That it's raised a couple of extra feet lowers my annual premium, as if there was a flood, the water would not be expected to get higher than 1 foot, so it would be highly unlikely that water will ever enter my home.
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A FIRM will generally show a community's base flood elevations, flood zones, and floodplain boundaries. As a property owner/renter, you can use this map to get a reliable indication of what flood zone you're in. However, maps are constantly being updated due to changes in geography, construction and mitigation activities, and meteorological events. Therefore, for a truly accurate determination, contact your insurance agent or company, or your community floodplain manager.
Flood Zones are determined by the FEMA map and it can run to thousands of dollars annually. Here is a link to their site : http://www.fema.gov/hazard/map/index.shtm.
An elevation certificate can help you avoid the cost of the expensive flood insurance if applicable.
I hope this helps.