Ebay offers Kryptonite Folding Bicycle Bike Lock Steel Compact Key Lock for $19.94 (reg. $34.99) with free shipping. 

Product Description: 
The Kryptonite Folding Lock offers ultimate convenience in bothportability, and lock-up functionality.  The included carrying bracketeasily mounts to the bicycle frame, and the swiveling 3mm steel barseasily maneuver through the bike frame and around an immovable objectlike a bike rack.  Folding locks are one of the most compact anduser-friendly lock styles available for your bicycle.