I have a feeling that part of it is development cost, plus the price of the processor(s). Plus it's a lot more material than other subs, at least in the case of the 600. These aren't your regular old "slap a large woofer or four in, put in a huge amp, and put it all in an enormous enclosure" type of subs. (I know, simplification...)

I am the Doctor, and THIS... is my SPOON!