I'm a pretty descent pan fisherman and have been doing great on Bluegill and Red Ears/Shellcrackers. I'm ok fishing for Crappie/Sacalait but have a lot more to learn and have decided to purchase/learn how to use a depth/fish finder. Most of the water that I fish are marshes, small tributaries and small rivers. I'm looking for advice on the best unit that I can purchase (reasonable) and learn how to use. Thanks