Consider how many more pieces there are in a freehub than a freewheel hub. I'm sure the manufacturing costs are moderately higher per unit, and the setup costs are *much* higher because a lot more tooling needs to be made.

Note the price difference between a Phil freehub and a Phil freewheel hub: $450 vs $180.

I'm not a hub manufacturer, so I can't tell how much of this difference is genuinely cost-related and how much is just "that's what the market will bear to pay." So, that's all I've got.