I have been waiting for something like this that is marinized. Cannot get a price yet but hopefully it will be under $50.
http://www.bluesea.com/products/1478/360_Panel_-_12V_DC_Socket_and_Dual_USB_Charger
http://www.bluesea.com/products/1478/360_Panel_-_12V_DC_Socket_and_Dual_USB_Charger