I think most of the Eagles and Humminbirds will do what you ask. In the deeper areas of the sound, many of the lower powered DF's will have trouble seeing the bottom, particularly at speed. That is rarely an issue with actually catching the fish. They'll almost all be able to see fish and bait to 200 feet or so, which covers most of the fishing I have done in the Sound.

Pretty much cost = power and resolution in this market. The cheaper units will have lower resolution and lower power. They're fine in shallower water and when you're not as concerned with what types of fish you are seeing. The midrange (200-300 dollar) units will work fine for PS salmon fishing, in my opinion.