Wind Turbines come in a wide range of sizes and prices. The world's largest, a SeaTitan 10MW, has rotors more than twice the length of a football field and generates a maximum of 10 megawatts. There are relatively smaller units, such as the Polaris 50kW and its approximately 19-foot diameter rotor, and even micro-turbine units with blades as small as 1 foot in diameter. Those can power only a few LED lightbulbs. The median cost for these units is about $10 million, which, considering the data range, is not a particularly useful statistic.
Cost per Unit of Output
While there is no available "average cost" of a wind turbine, there is, at least for large turbines, an average cost per megawatt. In 2015, it was about $2 million per megawatt. The SeaTitan 10MW, therefore, although not priced at the time, could cost in the neighborhood of $20 million.
Unit costs go up as size and capacity decline. In 2015, smaller units in the large estate/farm range of under 100 kilowatts cost from $3,000 to $8,000 per kilowatt. Depending on configuration -- for example, on whether the blades were fixed or variable -- the Polaris 50kW costs from $150,000 to $400,000. This is a per megawatt cost of about $3 million to $8 million.
At the bottom end of the price scale, the Aleko WG450A Wind Turbine Generator with a 450 Watt 24 Volt capacity was selling for $402 in 2015. Micro-turbines are largely for hobby purposes. Although the effective output costs of small off-the-shelf units are in the $1 million/ mW range -- theoretically competitive with larger units -- that figure doesn't cover a wind tower, the converter to go from 24 V dc to the necessary 110 V ac or the advisable storage batteries.
If you want to spend even less, DIY free plans are available from various online sources, such as Treehugger, which promises materials costs of about $30.
Only very large industrial wind turbines have megawatt costs that approach $100. They cost far more than an individual homeowner could likely afford, even if there were someplace to put such a large and noisy unit. Industrial wind turbines can be heard more than a mile away from their sources.
Zoning restrictions also limit rotor sizes. In Los Angeles County, for example, the wind tower cannot exceed 35 feet in height. For safety reasons, the likely limit of a turbine rotor in this environment is about 12 feet. A wind turbine with 12 foot diameter rotors, according to the calculations given in OtherPower, would generate only a little more than 400 watts in a 10 mph wind -- a hobby-sized wind turbine unless situated in a very high-wind area.
A considerably larger unit outputting 10KW is required to power a large home. The cost ranges from $50,000 to $80,000, exclusive of storage batteries. Tax incentives may reduce this cost, depending upon which state you live in and which ones are available when you buy a turbine.