We looked at putting one in our back yard, even with the power company required, by law, to buy back our excess at current rates, our payback was around 30 or 40 years! That wasn't nearly as big as these though.
Q. How big is the wind turbine?
A. Each 30 foot deep foundation required 850,000 pounds of concrete. The 15 foot diameter tubular steel tower measures 231 feet tall and weighs 98 tons. Hub height is 237 feet. Ground to blade tip measures 326 feet – taller than the Statue of Liberty. On top of the tower rests the 24 ton nacelle, the main body of the turbine that contains the gearbox and generator. The rotor, made up of the hub and three 87 foot long blades, is 179 feet in diameter and weighs 16.5 tons.
Q. Why does wind power cost more to generate?
A. Even though there are no fuel costs, generating electricity from wind is more expensive than more conventional means of generation like natural gas and coal primarily because the capital cost of the equipment is higher. This is generally true for most types of renewable energy. Another reason wind generated electricity currently costs more is that the energy found in wind is not as concentrated as it is in conventional gas and coal-fired processes. This means that more equipment is required to capture the same amount of energy.
http://www.smmpa.com/athome/windpwr_faq.html
Just do a yahoo search for cost of windpower