Hi
I run a 17' bassboat and have a Humminbird
fishfinder.
Unfortunately, the best finders I've seen are colour and sharp display and you'll not get a new one for 300.
Is your boat a runabout or open utility, aluminum etc. ? The reason I ask is that I'm considering using my FishinBuddy which is a battery powered removable fishfinder that goes on the gunwales of an aluminum car topper as a upfront finder on the bassboat. The Buddy is pretty good but not colour and not cutting edge but it does basic discovery of depth and cover. I'm not sure but I still think you can get one for under 200 ( maybe 130 or so ).
On Rice e.g. a fish locator is secondary to a depth and cover finder.
I've seen fish finders which go crazy displaying fish symbols, that I believe are false sensitivity readings.
Hope this helps give you some perspective