I'm in need of a new depth finder and need suggestions on what to get. It will be going on a 17.5 ft bass tracker. I've got a cheap hummingbird on the trolling motor that I plan on keeping but I currently don't have one by the steering wheel. I've never really used them much but for depth and temperature, but I really want to start learning and focusing on structure and how to locate the structure that displays on the screen in the water. I'd like to stay below 300 dollars if possible unless the next step up really makes a difference. Please give me some suggestions. Thanks

In your price range (not over $300) I'd seriously consider the Lowrance X125

(480x480 pixels - Monochrome - Waterproof - 5" screen - To 900 ft)

I'm currently using the X135 at $360 (in a word: Awesome!)

I like the fact that you called it a "Depth Sounder" and not a Fish Finder

Roger

I just got a HumminBird 581i with internal GPS for $350. It is an amazing unit for the price.

The 587ci will allow you to add the navionics chip and be able to stay on the drops on the river.  BPS has it for 470 and you can find the card for 119.  I know it's more than what you wanted, but it will seriously help you to stay where you need to fish the ledges.