There are several companies that provide flood, but they all charge the same amount based on your elevation and coverage level, so it doesn't matter what company you use. The federal government sets the prices, there is no competition. If you have an agent arranging your homeowners coverage, I'd suggest just letting them pick someone so you have one stop shopping.
You may find the HO coverage is the tougher nut right now, with all the insurance companies panicked about hurricanes. My insurer went belly up last year and I had to get a new policy, and I ended up paying 40% more than I had been paying because an 'excess carrier' is the only one who would touch waterfront. You might also get into a squeeze play between your bank and the insurance company, if you are taking a mortgage. Banks want to see low deductibles, but insurers are offering high windstorm deductibles. There's some negotiation that might have to happen there.
Another important point about flood insurance, one which my former agent never bothered to tell me about, which is why they are former: The maximum coverage available is 250k. Which is probably more than a flood loss you would have, so it's likely to be enough, even though your house is costing you more than that I'm sure. But you need to make sure you buy that maximum value, and if they raise the maximum, you raise with it. Because there is a provision in the flood program that says, if your house is insured for less than it's value and/or the maximum coverage available, the amount by which it is lower than that becomes an additional deductible which comes off of any loss, up front. In my case, the maximum had risen as well as my property value since I bought my house (I bought before the recent run up in prices) and I had only 215k in flood coverage, not realizing I needed to keep up with it. Suddenly I come to learn that the first 35k of any flood loss would have come out of my pocket because I was not fully insured. Now I have the max coverage and I have an agent who takes the time to keep track of such things for me.
If you are looking for a good agent, I use Sutton Agency in Islip. They understand waterfront issues, and they keep on top of things. They get all my insurance business now.
On the flood elevations, I've been told any good surveyor can handle that. There's one in Amityville named Harold Bausch whom everybody seems to use. However I understand the flood maps were revised a few years ago, and not revised for the better, so it may be tough to get some of the savings you hear people talk about. Good luck.
You are smart to get out in front on the insurance issues, well before you close.
Living on the water is great. There are a few hassles and insurance is a big one, but for me it's still worth it by a long shot.
