I don't have numbers for fire island, but take a look at the data from Eva creek wind farm.  It cost 93 million to put in, of which 13.4 million was state money, zero federal.  In the first quarter it supplanted 1.3 million gallons of Diesel fuel.  In rough numbers that is about 4 million dollars in one quarter.  The ROI is about 6-7 years.  Life span of a modern wind turbine is about 25 years, so looks like in pencils out pretty well.  See http://www.gvea.com/energy/evacreek