looking to select the right fish finder

While still shopping for my fist new kayak I thought I should do the same for a fish finder.  Here's the catch: being a self proclaimed cheap bastard I looked at my credit card rewards points and they have a selection of fish finders that I could have now without having to shell out a dime, just my accumulated points.  The ones offered that seem like are of the right caliber, in no particular order, are:
Garmin 150, 200, 300c and the hummingbird 718 and the piranhamax 170.  Which one of those would you guys deem suitable?  My needs are fresh and salt, as light as possible and easy to use.  I'm not really interested in GPS combo units just something simple that will work well.  The 300c gets great reviews but it seems the 200 has all the same features and power with a larger screen, though not color which I'm not sure is needed?  I know next to nothing about FF so school me on the goods and bads and what to look for.  Thanks all!

I have the Garmin 300c and the 550, my only regret on either unit is I didn't get GPS... I'm now looking for a separate handheld GPS so I can mark interesting structure or spots I caught fish ( which are few and few between).  Aside from that, the bigger screen on the 550 is nice. I originally thought the bigger unit would get in the way on the yak but it's been ok.

Just my $0.02 and a caveat that I'm a newbie to kayak fishing but these are my observations.

For me a fish finder with built in GPS is absolutely necessary for staying on top of a structure that you marked in any kind of drift, be it wind or current. You could buy a separate hand held GPS unit, but it would not be as simple to use. If you decide to buy a unit without built in GPS, make sure that you can add GPS functionality to it later as an option.

I find a color screen is easier to read the strength of the return. But then again, I am a noob when it comes to reading sonar returns.

For me a fish finder with built in GPS is absolutely necessary for staying on top of a structure that you marked in any kind of drift, be it wind or current. You could buy a separate hand held GPS unit, but it would not be as simple to use. If you decide to buy a unit without built in GPS, make sure that you can add GPS functionality to it later as an option.

I find a color screen is easier to read the strength of the return. But then again, I am a noob when it comes to reading sonar returns.

What he said

I like the 300c but was worried that it might be too small a screen.  Then again it's on a yak in your face and not on the other side of a larger boat.
As for GPS in general I guess I not strictly against it.  I'd love to have it but the FF offered don't have it.  Maybe I'll explore some other options.  What's a solid combo unit that won't break the bank?

Welcome To The Madness!
As a CheapAssBasturd myslef, I say go with cheapest ass FishFinder out there.This model was refered to me 5yrs ago. It has been through HELL and back=BOMB PROOF! One with a GPS and color will drain the batt faster. GPS aint that important until you get some time in OTW. I use a handheld Garmin that you can hike, bike and put in the car if needed. Keep it simple at first.
& Be safe