You need to take a look at the new Raymarine stand alone units (A series). Ray marine has introduced their digital fish finder technology into thier lower end stand alone models...at a fraction of the cost of what I paid for the full blown unit 2 years ago. (and is in your range I believe) . It is funny because 2 years ago the only way you could get the digital FF unit was to buy their full blown unit. They called me up after I had used the unit for a while to get "some information from the field". I told them I bought it mainly for the FF. I think they have a tremndous unit but the fact that you can only get the digital FF unit with a full blown $3K unit puts most small boat fisherman out of the picture, if they could offer this in a bare bone stand alone FF unit with out all the networking and interconnection stuff for less the 1K I think you would have a killer box. IMO that is what this new A series is.
These units dynamically adjust their own bandwidth so that the image is optimum, no surface clutter ever! and no knobs to tweek. You can clearly see bait and cleary see fish at the same time on the screen...IMO it is really an improvement over analog units. Its not a gimic.
When you compare the resolution of the sonar image to *anything else* out there in that range you will be very impressed. IMO you need to spend 10K or more to see images like that. The Furuno 600 is a very good, proven and rugged model but the display is a little small and the resolution of the image is blotchy compared to the new digital units, further it has been around for years...frankly I think it is dated. See it for yourself before you buy anything.
http://www.raymarine.com/raymarine/D...=766&Parent=40
more info here...click the clutter, clarity hassle links
http://www.raymarine.com/raymarine/d...=808&Parent=40
good luck
ad disclaimer: not schlepping stuff for a friend nor do I own stock in Raymarine or recieve any kick-backs from endorsing their products. I just like their gear.