They also break because they get old. It's awesome that it was just the belt. The last time I replaced the serpentine belt in my vehicle, the belt cost $35. If your Jeep has the 4.0l i6, you should replace the pulley at the same time. I think that was about $30 more. If you have the 4.7l V8, you need to replace the tensioner. I don't know how much that would be but it would probably be more expensive than the pulley on the 4.0.
Labor should be minimal. It's an easy fix. :)