Forget it. Get a crappy bike for the price you'd pay for a lock to ride to school. There's no way you should leave that bike locked up for any period of time. If you're going into a store, just be quick. Lean it against the glass and keep an eye on it. Someone broke into your apartment for your last bike. It's soooo easy to steal one broad daylight on the street.
I have two bikes for this reason specifically. It's not worth the stress of locking up your baby to a pole. Plus the lock will scratch the paint
