Since you are a beginner, the questions are easy to answer:
Buy used. You can pick up a great starter bike (500-600cc or less) for a couple grand, and sell it for nearly the same when you are ready to move up.
If you are interested in sport bikes, they take more than a couple hours to master. Take your time, and don't do any stupid bullshit to get yourself hurt.
Also, contact your local DMV about a Motorcycle Saftey course. It is well worth it, and the insurance savings are nice to boot.
As for a bike, since you are interested in Kawasaki, I would recommend a used Ninja 250R or 500R. Any bigger as a beginner, you are just asking for trouble.
(A brand new 250R is $3,000 and a 500R is $4,799. Used is much cheaper.)
Yamaha, Honda and Suzuki have similar bikes.
Oh yeah, expect to drop the bike, or lay it down a couple times too.