I am 18 and never bought a bike and i want one. I want to get either a used cbr600 or gsxr600 from 04'-07'. But how much should your monthly income be to buy such a bike?
Motorcycles are a lot cheaper to keep and maintain than vehicles. Here in the state of Florida you do not need to carry insurance to drive them. The tags and registration are cheaper to register than vehicles. And motorcycles are usually way better on gas than most all vehicles on the road today. Although used motorcycles are sometimes harder to finance than used motorcycles. But if you can find a 600cc bike for $5K-$6K then your monthly payments would be around $80-$90 per month. A good rule of thumb to find a ballpark for your monthly payments is $16 per thousand dollar borrowed. a $6,000 loan would run you about $96 per month.
Keep in mind it is a LOT harder to use a motorcycle as your sole transportation because you run into a lot of different challenges. Groceries are hard to carry home on a motorcycle. It is hard to go out to social events that require you to dress up on a motorcycle. And it also becomes challenging to ride in inclimate weather ie. rain, cold, snow, ice, etc...
However the rewards can be worth it. Parking is a LOT easier with a motorcycle and a lot of times makes traffic a lot easier as well. You save a lot of money on gas. And you also have some fun out of otherwise boring commutes. I have a motorcycle and a car and I did an experiment for 2 weeks where I parked my car and only used my motorcycle for my transportation needs. It is a lot harder than it sounds.