Look in the classified section here in marine electronics. Always a great deal to be had on used models. I prefer Lowrance. I would not get anything smaller than a 7' model with the standard 83/200 trans. Don't need all that side scan stuff. Garmin also makes a good machine.
i bought a used boat that had a 5 inch screen lowrance. great unit but kinda small, instead of replacing it with a bigger unit i just mounted a 10 inch tablet running navionics on the side. I like it so much more that the regular chartplotter it works double duty as it has all my music on there.