I have no idea on the cost but you can call them directly. The phone number is on the web page.
After chasing down as many options that were findable on the web, I decided the best sounding, least time consuming instal and most out of the way for storage approch is to use the JL Audio Stalthbox.
Afterall, the box is supose to be tuned for the 4runner in the first place.
I found a better use of time was to insolate the car via Dynomat and carpet. That alone will make an average sub sound better.
Good luck.