Rich, are you saying that the "upgrade" to the 520c, if ordered from Skeeter is $649. Standard is the X135 in dash upgradable to the 520. If Skeeter charges $649 then that's the list for the unit to begain with. Where does the $400 for the X135 thats standard on the boat go? I hope that you're saying that you can add the 520, then move the X135 forward for that price, not just the "upgrade" of the dash unit price. If so what's Skeeter's upgrade dash price only?