The reason that thing is going for $2,500 is because it is a collector's item. Only someone with one of those "antique" subs would have any interest in that thing. There are a couple of web sites for people interested in vintage audio equipment:
The people who actually buy from these sites know how much money it takes to engage in vintage audio. Some of the greatest pieces ever include the JBL Everest, and there are many more that make those who collect (and use) these items just drool...
I think I'd go with some 18" drivers that claim 54mm Xmax:RE Audio XXX18D2
The customer reviews at SonicElectronix are great for this one. One person claims he blew out his window in the car; another that he has six of them in a van
There's a handful of AVS'ers that are rockin' the RE drivers in subs. One 4x manifold user, another user employs 4 small sealed in a typical room. Those drives are highly vetted, solid performers. That cone travel comes in handy for the deepest freqs, as every halving of freq, requires a quadrupling of travel to maintain similar playback level.
Yeah, those, if I recall correctly, enjoyed a little run in time whereby they had a modicum of popularity in studio baffle wall, soffited subwoofer use. I recall more than one build with these,...circa mid 80's-mid 90's perhaps. I remember one such that had two per side in a wonderfully nice, Scandinavian studio. More than ample displacement for studio music playback.