It's a really good deal - a Bosch alternator for 160 bucks! New ones cost 400+. How long is the warranty on that rebuilt one? 'Cause you can rebuild your old one for about 70$ - just search for "alternators" in yellow pages - and u'll find a few companies that do that. They will replace the brushes (those wear out and voltage drops to the extent of not being able to charge the battery) - 30$, and if necessary, voltage regulator if it's gone.
You can also try junkyards for used ones, or this site (which gives a summary of all inventory on nearby junkyards): http://car-part.com/