I got my extender on eBay, too. It was from a truck with a wider bed and needed to be adjusted narrower for the Ranger - easy.
I had to get the pivot brackets separately since they weren't included with the extender. A pivot kit from AMP Research cost me $10 including shipping.
EDIT: Be careful when shopping for used ones. Some of the OEM extenders that are factory options on new vehicles are not
adjustable for width and usually use a different pivot arrangement. Not only does this limit what they will fit, It also makes them very expensive to ship, due to oversize dimensions. The universal, adjustable aftermarket extenders can be broken down into several pieces for shipping in an ordinary sized box.