Didn't see this post until now.
If your only using it for running a probe, I would not purchase anything overly expesive. No need for an electric rigger. Your trolling speeds are not really all that fast so you can get by with a smaller weight cannon ball as you will have minimal kickback of deflection. Retrieving that should be pretty easy with a hand crank. Although I prefer "Big Jon" (personal preference), I have also owned Cannon manual Uni-Troll riggers. I think you can pick one up for around $140.00 that would have no troubles.
I only have experience witht he fish hawk as that is the preference of choice for great lakes fishing. Fish Hawk provides great speed and tempurature readings at the cannon ball. The older probes required a 9 volt battery to be inserted. We always unpluged when not in use. Remember that you will need an additional transducer to read the probe and send to your helm mounted readout. Should give you surface temp and speed as well as speed and temp at the ball. Valuable tool in the great lakes with current, wind and waves.
I have OCD "Obsessive Crappie Disorder"