I was in your same shoes about 4 years ago when I decided to get into the sport. I started out in a Dagger RPM. These are great boats for beginners as many instructors still use them in pool classes to teach beginners how to roll. This would be a good boat that you could purchase used for a few hundred bucks, and not to mention they have been around since the 90's backing up that reputation. But with larger volume river runner/creek boats emerging every year, my best advice would be to go with a Liquid Logic Remix like mentioned in previous post. I think that they are great boats for anyone looking to start the sport, or the person who is ready to huck a waterfall. The RPM is just too slender in the stern causing it to slide out more on you in faster moving water. Not to mention the Remix outfitting is leading the pack in comfort.
I would strongly advise you to stay away from play boats. I truly believe that confidence is built by being in a more stable boat with larger bow/stern.