I have a small jon boat I use to fish watersheds and small lakes. I'm looking for a depthfinder/fish finder for it. What is the best available for around $100. I'm looking for something that I can have confidence in, when it shows fish that there are fish there. If it could show the stucture (ie, stumps, rocks, brushpiles) that would be great too. I don't know much about todays electronics and get lost when reserching myself.