Depending on the location of your property it may be in a socalled flood plane. Banks require flood insurance across the board. Without a lein on your property it is your decision. Remeber - flood insurance has to be in effect a minimum of 30 days to apply.
Premiums depend on a number of factors - location, age, previous history of property, size, appraisal, type of coverage.
Pick something off a realtor's website and run through a number of insurance quotes. Google is your best friend. Call for help if you need it.
One of your issues will be lack of insurance and credit history.