What is Unity

What is unity and how much does it cost?

What is unity
I’m assuming you mean:
http://unity3d.com/unity
http://en.wikipedia.org/wiki/Unity_(game_engine)

and how much does it cost?

Unity is free http://unity3d.com/unity/download
Unity Pro https://store.unity3d.com/products/pricing
http://unity3d.com/unity/licenses