Won't get into the specs on the transducers.

Buying new $100 difference on Garmin Website. If buying from a forum classified there is a huge price difference. There are so many of the GT54s out there you shouldn't have any problem finding one for less than a hundred bucks. I have several myself. Guys were buying the Ultras with the GT54 packages from Cabela's/Bass pro with the GT54 on sale for livescope only or second screens so they didn't need the transducer.