My suggestion would be a Honda XR150L
Honda XR150L The low seat height, light weight, and unintimidating power level will allow you to learn how to survive motorcycling without breaking the bank. It is a capable trail rider, fairly durable, with a strong dealer network to help you out along the way.
Sign up and attend a sanctioned MSF rider training class if you plan on riding on the road. Trees and shrubs are predictable, Oscar Grope behind the wheel of a 4000# four wheeled vehicle, not so much.