Peerless SWR 315 (can be found at Parts Express) will work fine in 3 cu.ft. closed box - Q will be 0.85, resonance ~42Hz & -3dB at ~38Hz. With up to 6dB equalising you will get to ~25Hz, very nice. The Peerless unit has a peak to peak linear excursion of 18mm (~3/4"), sensitivity ~89dB. And, the Peerless driver is affordable!

Another option would be the Eminence LAB 12 - good parameters for reflex box of 3 cu.ft. Tuned to 24Hz it should get you to 25Hz without the need for any equalising. The LAB 12's linear peak to peak excursion (13mm ~½") isn't as large as the above Peerless, but the reflex loading will more than make up for that. The LAB 12 isn't quite as sensitive & also more expensive, though.

Just a couple of ideas - there's MANY 12" drivers out there that will do a nice job in that box size.