If it is working 100% then the driver is worth $200 and the amp 1300 was sold for $450 new. eD's best quality were their cabinets so that is another $150. So $400 with a 100% working sub is very good. Try to find any sub for $400 with amp. Most are not very good.
I just sold my A7s-450 to my friend, as I purchased MKTheater's setup in his avatar. I got $500 for it with the Dayton plate amplifier. As James posted, $400 is an excellent deal if the subwoofer is in working order. The only possible issue I see forthcoming would be with the amplifier, however, there are members on here that can help you with getting it repaired if need be.