Which Fish Finder/Chartplotter

Going to be fishing inshore want to mount this on the console and essentially mostly use it for navigation. The budget is ~$500, the cheaper the better, and it doesn't have to be the newest unit. Most importantly I want to be able to use Navionics, or similar (what else is good out there?), with decent marsh maps. Equally important, I want to be able to create routes on Google Earth and import them to the unit for use in the marsh. Somewhat important, being able to mark spots from the unit, not glitchy in shallow water, have a 7" screen, and be relatively "snappy" when switching between things/zooming/etc. The least important thing would be the sonar resolution. I think I would prefer side scan to down scan but would be interested in opinion on that for inshore fishing.