2d broadband sonar, Down Imaging, and Side Imaging sonar are ALL best used while "moving" ... as you will get the better image in so doing. 2d may not be quite as distorted as DI or SI, when stationary, but it will be a distorted image to a degree.
I use a DI unit on my trolling motor ... see what I'm passing over or return to a previously marked waypoint ... then if I want to remain stationary over it or slowly move around/over it, I stop paying as much attention to the screen & pay more attention to my poles/line. But, being as it has GPS capability ... if I wander off from the spot, I have it marked on the basemap and can return to it. If I were only going to go to a visible cover spot & tie off or anchor and fish, I probably wouldn't even bother to spend the money to have a depth finder, of any sort.
Something like the Lowrance Elite 5x HDI unit might be all you need. It's a 2d/DI combo unit, where you can use the two sonar systems by themselves or together on a split screen. They're currently being sold at around $200.
Similar Humminbird units (such as the 561, or 571 HD DI) are in the same general price range ($190-$260), but are greyscale only (b/w), not color units.
Down Image/2d combos work well for those that want the dual coverage beams. Plus, the DI screen image gives you a picture quality rendition of what the 2d "finger painting" image really is .. without the need of long term experience in interpreting the 2d image. But, one has to be aware of the difference in the shapes of 2d & DI sonar beams, and how the DI beam relates to the direction the trolling motor is pointing.
(* prices taken from current Cabela's ads, and may be found cheaper through other sources)
... cp