Well, like the OP already suggested, the materials used for the cooking pot are far lighter than heavy cast iron.

I just need to look in my kitchen cabinets to see the difference between a normal cooking pot (thin sheet of stainless steel/aluminium/etc) and a Dutch oven (solid iron, at least half a cm thick on all sides). With a content of 3,8 litres, they'll probably be the same size - but the materials and thickness can easily explain the weight and cost difference.