help picking out a sonar unit

I recently bought a fishing style kayak to use on some rivers and lakes in my area and I am looking for a decent sonar unit to put on it. Since I’m dealing with a much smaller amount of space, I’m looking to get one of the more compact models, and since I will only be using it occasionally I don’t want to spend a ton of cash either. I was thinking something between two and three hundred would work just fine. Anyone have any suggestions? I don’t really need GPS, but it would be nice as a luxury. Thanks for any info!