As far as I know you can't buy just side imaging. You can buy down imaging. Side imaging is good for scouting and finding various bottom structures and cover. It is not easy to use unless you have the big tv screen.
Down imaging is what I run most of the time. I like it better than 2d sonar because it is easier for me to interpret.
If you are not in a hurry, go to bassboatcentral and look at the Lowrance and Humminbird screen shots. In some of them you can actually see the fish among tree limbs that you can actually count.
I'd go over to Council Bluffs and have a look at Bass Pro if it were me.