Ninja 250. Fast enough to be a thrill and dirt cheap. If you are a bigger guy, then a 500-600cc bike would be okay too, but a modern 600cc more than enough to get you killed fast. Take the course, and don't be cocky: bikes are hard to ride, no matter who you are. Oh, get full gear! If you want to look cool, get a nice set of bright leathers and boots/gloves, etc. Dress for the crash, not for the ride!