I bought an Eagle Fishmark 320 that sells in a portable option. The portable option comes with a suction cup transducer mount, all cables, the sonar unit, and a handy carrying case which the unit mounts on top off and then houses both a large power cell battery and your cables. Battery and charger are extra. Picked up my portable unit, battery, and the charger for $270 on sale. One could always permanently mount the unit onto a boat afterwards by simply buying a few mounting brackets.
Eagle has a few cheaper portable units but they do not house the battery cells in the carrying case and there are less features/power on the unit itself.
Awesome unit and I have no issues finding fish that's for sure. Catching them on the other hand is a little more difficult.