Below are two locks that I picked up at my local dollar store. The one on the left was $4 or $5. The one on the right was $1. If you are going to lock up your bike for an extended period of time I would recommend a U-lock, which can run you around $20. For a high quality U-lock, you can expect to pay more.
However, U-locks are heavy and add to the overall weight you carry on your ride. The locks here are affordable and lightweight. Ok, the one of the left is a little heavier (but not as much as a U-lock). The one on the right is great for locking up your bike outside the grocery store. It provides enough of a deterrent to prevent someone from walking away with your bike. At this price, you have no excuses for not carrying a cable lock.
The one on the left is more substantial. The cable is encased in thick rubber plastic type material. The cable inside looks to be woven three or four times. I can see wire cutters having a hard time cutting this cable lock. This lock is good for going inside the mall or seeing a movie for 3-4 hours.
Go to your local dollar store and check these out. I picked them in red color because I figured the "drive by" thiefs will notice that my bike is locked.
