Whats a cheap auto insurance for teens?

I've a buddy that has a supplementary vehicle. He let the vehicle is driven by me. He's a-protection on the car and that I do not have any car  insurance    before. Is it fine to push? Liability  insurance   comes with owners or automobiles?
"I am 16 years old but will undoubtedly be 17 the following month. Thus lets say Im 17 for the present time. Im thinking of buying a BMW z3 because they are pretty cheap and really great vehicles