i've got a garmin 300c, its a small unit that does a decent job, i paid around$250 for it but think they have dropped in price a little bit :-/ if your fishing the icw up here all you need is a basic unit that will give you accurate depth measurements so you can find the holes, no need to go broke buying much more imo
I don't own a fish finder, but have been looking into them. The humming bird fishing buddy series interested me. It's portable and self contained, which I like since I fish mostly water 8" or shallower. Give it a look.