1. There is no average cost. Never mind that we don't know what size turbine you want to make, the price will vary drasticly depending on how much work you plan to do yourself and on the materials used, especially since so many parts for these turbines can be made from used materials. HAWT or VAWT? What size of tower?

2. Another very vague question. When you say "transfer to your house" do you mean a Grid tied system, separate battery and inverter system or do you just want to run some 12v loads? Or maybe you just want to made a windmill to strictly heat water in your home?

I figure a 4 or 5' system could be built for under $500.  Maybe well under $500 if you have good scrounging skills (used golf cart batteries, used well drilling pipe for the tower, used inverter, etc).

A 4000^2' house doesn't tell anything.
If you have 4 kids with their own TVs running while they do homework/internet on desktop computers 10 hours a day, then that's a lot more power than a single bookworm.

Anyway.  A 10' will not power your whole home.  I doubt it will be cost effective, even if you CAN build something big enough to power the whole house.
I worked out the cost to run an LED desk lamp, and the battery cost more than the electric it would save over the battery's lifetime.

TomW has a lot of power now, and he is getting close to off-grid,
http://www.fieldlines.com/story/2009/11/9/757/06197

Bigger is cheaper, per watt.  Something like a 17' may take a good bite out of the electric bill, but I am not sure most people would really see any money saved.
I do not think building a 17' for the first windmill is a good idea.  At all.

 If you want an extensive hobby that will give you the satisfaction of generating your own electricity, then investigate further.Running an entire household off of one homebuilt windmill will not happen. Look at your last utility bill and get a sense of how much power you would need to generate. You'll also need to know the average windspeed at your site to determine what sort of output to expect.

 It is extremely easy to put more that 2 grand into a windmill.

 You'll be much better off SAVING electricity than trying to produce your own, I'll bet you could cut your electric bill in 1/2 without giving up anything essential. Of course, saving electricity is the first step in becoming a good RE'er..ya don't have to make what you don't use.

 I'm not trying to discourage you, just educate you. The electricity generated by a windmill is not free! It's just pre-paid.

 A lot of people just run part of their household off a windmill, say their computer set-up.

 There are a ton of sites on how to save energy, how to insulate, how to generate hot water off sun power, etc. I'd say generating electricity on your own should be the last step in a plan to become energy self-relaint.

 For instance a DHW (domestic hot water) system can be built for anywhere from $500.00 to $2,000 and up that would provide a lot of your hot water needs, eliminating that part of your utility bill, this will have a faster payback than building a windmill.