I went through the same thing a month or so ago for my kayak. The answer depends on what you want to do.
For me, my fishing is in shallow creeks like Tingalpa Ck and places like Wellington Pt and out front of Manly Marina. The water is pretty shallow and there is not a lot of structure like fallen trees, etc, that I'm trying to find fish amongst. So for me it meant that downvu/down imaging was not really of any value and neither was chirp. I also reckon that a sounder on a kayak is going to have a relatively short life compared to one mounted safely within the cabin of a boat. This meant that I didn't want to spent big $.
I ended up with a Lowrance Elite 3X. For $130 it does everything I want. the elite 4X has bigger screen and better resolution I think but I decided I was better off spending $130 than $220 for the 4X. From what I could gather the Garmin 301 series is better quality than the Lowrance (and is reflected in the price). I reckon if and when my 3X dies I will look at the Garmin 301C. I did notice that the Humminbirds seemed to be higher priced than the others.