AS far as the box goes....I would say it depends on how crafty you are. They really aren't hard to make, but you have to make sure you built them to spec with your sub (aka how much air it needs). You probably shouldn't use just any old "wood"...you'll want to use maybe a medium density fiber board. You may check ebay to see if you can find a pre-assembled one for less money.
BTW....who makes DUAL or is it a new company....I know it is one of the cheaper brands that Best Buy just started carrying but that is all I know.
