First of all sign up for & take the MSF Course where you will learn the basics in how to ride a m/c along with possibly staying alive.
I try to suggest one of the 500cc vertical twins by Suzuki or Kawasaki as they are in a regular riding position that has been used since the early 20s & still the most used form of riding.
Both bikes are almost bullet proof in their construction, less in cost then a sportbike & less for insurance.
Another advantage is the engines have a nice mid-range power rather then being a peaking engine----believe me the torque of a m/c engine is so important to one new to riding. At the change of a light to green they are faster then most of the cages & can scoot you up to almost 100mph.
After you have got the full feel of that bike & understand far, far more about m/cing you will then know which way you want to go for your next bike be it a larger bike like 750 to 1000cc of around the same design or 600cc sportbike, or Cruiser.
Remember you will have to put money aside for crash helmet & other good protective riding gear FOR a two wheeled m/c is not self-balance nor does it have all the protection of a cage.