Depends on the bike. V-twin cruisers get anywhere from 30-70mpg depending on the size and make. Also, some bikes don't share oil with the crankcase and the clutch. Japanese bikes from anytime in the 90's and Harleys/Buells from '84-'98 are bulletproof, so don't worry about repairs. Chainlube (or not if you're on a Buell), tires, oil, and maybe a clutch here and there are all you're going to need. Go take the MSF course!