Well you can spend as much as you want! There are many variables. The very first thing that you will want to do is check your local restrictions. Many areas have height restrictions and some even have amount of property that it will be on. For instance, where I live you must have 5 acres to have a wind turbine to produce your own electricity. Of course that would be for a huge tower to power my entire house. I would be allowed to have a small wind power turbine.
So the next thing that you must ask yourself is about your skill level and how much you want to save.
I have seen do it yourselfers put up 20 foot towers and power everything. I have seen small turbines that just provide enough electricity to run a shop. And that was in a very small yard!
So if you have plenty of property and money, you could hire someone to come in and erect a wind turbine tower for you.The cost of wind power at this level would be very expensive.A few thousand dollars. I have seen systems up to $200,000.00. Of course that would be a commercial size system. At this level you will want to do a lot of math. I would recommend getting a professional involved. You would need to check the payback time. In other words how long would it take to pay for the system in savings. And do not forget to check for tax incentives and/or rebates. Most areas have incentives for renewable energy projects.
So if you are a do it yourselfer and have some time, you can probably put a system together for around $200.00 or less. Will it power your whole house? Probably not. But you could save up to 80% on your energy bill!