In the state of Oregon you must be a minimum of 16 years of age and you must have a class C (or higher) drivers license in order to apply for your motorcycle permit. You must not have any limitations, suspensions, cancellations or revokations on your license in the state of Oregon or any other state. You must obtain the signature of your legal guardian on your motorcycle permit application.
You must provide proof of your full legal name, your identity and date of birth, your social security number and your Oregon residential address. (Visit the website for a list of acceptable proofs of address. Honestly, having your legal guardian, such as your Mom or Dad, come to the DMV with you and providing a utility bill with THEIR first and last name on it, or providing their license with the address matching where you live on it, would be the easiest solution!
The Harley Davidson 2010 883cc Sportster is a light weight, fast motorcycle purchased my many beginners. However, unless you can find it used, your not going to get it for less than 15 grand. I recommend buying a Yamaha sport, or something similar. Buy it used if necessary. For 2-3 grand the bike is going to be in EXCELLENT shape!
Motorcycle insurance is pretty cheap in general. Considering your age and gender, the type of bike you are looking to drive and the fact that you will have had your motorcycle license for less than 4 years, your insurance rate would be roughly $300-500.00 per year.