Being able to find baitfish can be a pretty important deal, especially if you’re fishing suspended fish very much at all. So a depth finder that can pick out either suspended bait, or baitfish on the bottom closer to structure is definitely a plus.
The good news is, if you’re thinking of a new depthfinder, but haven’t shopped for them in a while, you’re going to be pretty pleasantly surprised at the quality and capability of even the more moderately priced units these days. Not sure what your budget range might be, but especially if you’re just looking for a pure sonar, without any GPS capability, you can get a very good unit for well under $300 – sometimes well under $200. A unit like the Lowrance x-125 is a very good, easy to read unit that is more than capable of marking baitfish, and it’s not too expensive. I ran an x-125 on my bowmount last year and was pretty pleased. You can also look at Eagle units, which are very solid as well.
From there, the sky’s the limit on what you want to spend, but the main thing to keep in mind is a unit’s power has a lot to do with how well it’ll mark baitfish (and how clearly it’ll show you weedgrowth, bottom content, etc.). Look for units with higher peak-to-peak power, and you’re headed in the right direction.