I am currently in the market for a new fish finder. I have never really used one so fairly new to them. How exactly do they work? Are they sending the beam straight down or is it in front of you? How wide is the area that it is actullay picking up few feet? I would like to pick up stucture,water temp and depth. I am not looking for anything really nice. ANy suggestion on one. Would like to stay within about $300 thanks