Here's a used transducer on eBay:
http://cgi.ebay.ca/HUMMINBIRD-HIGH-D...QQcmdZViewItem
Otherwise, it might be cheaper to look for a Humminbird PiranhaMax 10 or 20 on sale. I saw one on clearance at Sport Chalet or Sport Mart for $60 about a month ago. It looks like they use the same transducer.
TL
Rex