Go fish...
Definitely get the fish finder for the following logical reasons:1. Depth sounders only tell you the depth. Period. 2. Fish finders will not only tell you the depth, but with a little practice and tuning, it will tell you what kind of bottom you have for selecting the proper anchors, what kind of slope to the bottom is under your boat, if there are any trees, wrecks or other obstructions that might endanger your rode or boat at lower tide levels, and if you like to fish, if there are fish down there, and at how many feet. The limitation to most fish finders is maximum depth, compared to high end depth finders, but most people don't care beyond 500 ft. anyway.