I have a cheap one. I normally fish shallow water, so with the narrow cone, I don't normally see fish. I really want to see the bottom composition, and how deep it is, plus water temp. My transducer is mounted internally, GOOP'ed onto the inside of the hull. I don't get true, real-time temp readings, but after an hour or so, it settles down.

I use a 8-cell, AA battery tray from Radio Shack as a power source. This batter tray uses 9v battery clips, so I bought a bag of them as well. All totaled, I spent about $5 at the Shack. I got a Pelican 1010 (or is it a 1020?) box, the smallest they have, yellow, and you can't see through the lid. I drilled a hole, and inserted the power supply wire for the FF. I GOOP'ed that connection as well, but really need to get a rubber gasket for it. I wired a 3 amp in-line fuse into the postive lead, then attached the 9v clip. Put some batteries in it, and she fires right up!

I usually get most of a summer fishing season on one set of AA's.