Where to find adequate woofer replacement for PSB

I have an old set of PSB 50 MKII's that I just love.

One of the woofers has had something gone wrong in that it vibrates like crazy during heavy speech or voice.

The woofer and it's rubber surround seem perfectly fine. The problem seems to be that very center 1" area and the little paper tube that surrounds that metal center. The paper(ish) tube connects to that thin layer of foam (?) that is just in front of the magnet.
(a picture would be worth a thousand words here, eh?)

PSB wants several hundred dollars for a replacement.

Does anyone have any suggestions for a more cost effective fix or replacement, short of buying new speakers? :)

I appreciate the help.