I just had a SuperGlide 4100 installed with under bed rails and king pin capture plate. Total cost was $2200 installed. Installation cost was $300 so $1900 for hitch, rails and capture plate. The under bed rails are considerably higher priced than the above rails. Furthermore, the rail kit is specific to the truck its being installed in. So buying used you have to find one from an similar truck.
The capture plate is required and the exact one you'll need depends on which trailer you purchase and which king pin that manufacture uses. Cost for capture plates new are about $200.
The dealer also installed a 7 wire outlet in the bed of my truck that T'd off my existing bumper connector. Cost for that was $95 installed.
