Ebay offers Kryptonite Folding Bicycle Lock for $20.99 (reg. $34.99) with free shipping.

Product Description:
The Kryptonite Folding Lock offers ultimate convenience in both portability, and lock-up functionality.  The included carrying bracket easily mounts to the bicycle frame, and the swiveling 3mm steel bars easily maneuver through the bike frame and around an immovable object like a bike rack.  Folding locks are one of the most compact and user-friendly lock styles available for your bicycle.