Kev,

I'll try to post a pic of my setup later. My advice would be to look for a good used Lowrance like an LMS-332c or similar. Most bass boats come with a graph like this standard at the console, and many guys wind up upgrading them to larger units. Check westernbass.com, craigslist, or ebay. You might be able to get a nice little color unit like this for $200 or so.

Rig it on a 12v battery from Cabelas like . On sale right now conveniently... Then round up a transom mount transducer bracket. I have one that Cabelas sells. Seems like the price has about doubled since I bought it 10 years ago. Like Phil pointed out, some of the Bass-n-Tubes guys have rigged similar ones from pvc and other materials.

The only aspect that's missing here is a place to mount it. Need to think of something there, or just set it on a bag or a cushion.