Martin Luther King had a dream and so does Joe W.
I will sell my 2003 196 Superfisherman for that price with twice the engine size and absolutely fully loaded.
Use your cell phone. Just calibrate it on a level surface before you get on board.
Still, not sure why this is so critical. Speed and temp is much more critical than what depth the lure is at. A few feet won't make a difference once you find the proper temp.
Do you think that the dipsey depths are dialed in? They would be affected by so much more.
The guy selling it is also full of it. My buddy responded to the ad and asked some questions on the repairs and was told the transom repair cost $3500. Not sure why the guy would have to lie about things.
Just be honest with your request as you've been "helping your son out with his boat" with reasonably priced electronics for years. Somehow that help includes reselling electronics that you purchased at a cheap price.