if you are talking about more conventional then remember the transducer is more important than the head unit. The transducer I was after turned out to be £5000 on it's own for my Raymarine!!!
Hey Manos
Reson Seabat should do you nicely http://www.reson.com/sw1122.asp
used one of the earlier versions of this to find a lost sensor in the bottom of Plymouth sound and it was only 1m x 10cm x 10 cm.
You starting another side line or is this just for pleasure ?
good luck
James