Subwoofer for classical music listener

Thanks for the responses.
I have a 25'x23' foot room, a much modified vintage system with great impact  which, to me, is perfectly balanced for classical except for ultra low bass (e.g. organ).
 System:
Modified Dalquist DQ 20 speakers, modified Nuforce amps, modified vintage CJ preamp, Theta DAC, Oppo BluRay player used as transport, Rega RP3 turntable, Grado Sonata cartridge.
I would like to spend around $1000, more or less (preferably less.)

A pair of Vandersteen 2wq's would be my recommendation, though a pair of 2w's would probably be as good.
B

Gallo TR3 is 799$ new, used ones don’t show up on here(a good thing). One sub is all that’s needed to play the odd organ piece and relieve mains from
burdens below say 80Hz which brings more clarity which is always needed .
I’ve heard Vandy subs but IMO Gallo beats them.
If your Oppo is less than a 105 a Cambridge CXC transport(449$) might do more for system than sub .
Might do more if it is a 105 .

Some say two subs evens out bass in room. I've found one is enough IF you get the placement right .

The B&W DB1 is a really great sub..... dual 12" drivers, easy to integrate and built like a rock.  Good aesthetics too.  They have an updated version coming out this summer with several changes to the amps and driver material, but also giving the user ability to adjust the parameters via an ios app.  I listen to all types of music, including lots of classical skewed heavily towards piano, and I get the most enjoyment from my sub specifically on classical.  I'm sure there are many other good choices in subs but I can't imagine one meaningfully better than the DB1.