+1 for craigslist. I have bought one bike and sold two on there and it was easy as pie. I had a friend that sold his beat up old yamaha virago four hours after he put it on craigslist.
I had another friend that bought a $400 dollar POS suzuki 400cc roadbike from the early 80's, road it around Alaska for a few months while he was working there, sold it and got most of his money back, got a ride down to Portland Oregon with a coworker and bought another bike there, rode it down to California and sold it so he could go back to college in Hawaii.
Yes, it can cost a bit to get decent riding gear, but once you have it you are good to go. Start with a super cheap older bike (that runs) and have a ball with it while you build up your skills and figure out what kind of riding you like. Then when you've got some cash saved up, sell it and buy something decent in the category you desire.
I started with a 750cc cruiser given to me by my dad, which was great to learn on. I decided that I liked sportier riding, so I got a 600cc sportbike next and sold the cruiser (sold cruiser for $3000, bought sportbike for $3000), and had a blast learning how to ride fast. Eventually I decided that I wanted a more practical, more robust bike, and I sold the sportbike for $2700 and bought my current bike (2003 suzuki v-strom 1000... kind of like an overgrown dualsport with hard luggage) with tons of extras for $4800.
Riding has been the biggest influence on my life for the last four years since I've learned to ride.
