Looks like they're $750 new so $400 is reasonable if there's no shipping fees. Your other option is to bin it and get 2 subs like REL T5x etc.
Repair or replace my subwoofer
I have an earthquake supernova mkiv subwoofer which is 20 yrs old and has now started making horrible static noises when turned on. Earthquake said they will replace the panel for $400 or I could simply buy a new one. I don’t know enough about what “makes” a good subwoofer, the mechanics or the electronics? Which way should I go?