i'm going to purchase a depth finder/gps unit for my self for christmas...cause i deserve it !! i've been told that garmin is the way to go..i'm looking at the 398or maybe the520..those could be the wrong numbers any way does anyone have any insight as to if it would be cheaper to wait untill march or so..also whats the difference between a chart plotter and gps..this is only a recreational boat no major off shore use..mostly the long island sound..any suggestions