Current Inexpensive sub that can get it done cheap

Well engineered ported designs as good as sealed designs IMHO.
Each has its tradeoffs -
Sealed boxes have issues mores on an issue with standing internal standing waves being feedback to the speaker cones. Ported designs exhibit other possible (arguably) tradeoffs. I’ve heard designs of both schools that sound excellent. All rooms exhibit ‘modes’ – they just occur at differ frequencies (they all will fall into the subwoofer range). Different speaker drivers end to work better in different designs depending on several factors. A major one is the ‘Q’ of a driver. The bottom line is that the driver needs to match the box design. One is not necessarily better than the other. Room modes and reflections also occur at all other audible frequencies. There are quite a few places on the WWW that will explain how to calculate them.

If you don't mind buying used, there is a Paradigm Servo 15a with x30 crossover for sale now that would definitely fill the bill. No association with the seller.

I would second the Paradigm Servos no matter which model.
IMHO they are exceptional for the money.

If you can find a Definitive powerfield 12 or 15 it would definately fit the bill.
I have had a 12" for about 10 years and I am listening to it as I type this.
Built to last, it also sounds very, very good, just not as fast as the Paradigm servos.
Sounds really good on movies and music as well.

if 'snappy' means clean, fast, accurate you want a sealed or servo design, though you will give up a bit of maximum volume and/or extension.

you might consider some of the internet directs: epik empire (2x15", sealed) or legend (2x12", sealed), or rhythmik F15 (1x15", servo).

i have a single empire in a 3300ft^3 theater, and i am quite pleased. it stays ruler flat to 20hz in my room. a 2nd will makes its way here before too long. there is absolutely no comparison with the outlaw lfm-1ex (1x12", ported) that it replaced.

to help alleviate the effects of standing waves, 2 smaller subs is almost always better than a single. also, you might want a sub eq (SVS as-eq1 / velodyne sms-1 / antimode 8033)...they can make a world of difference. i have the SVS and it was worth every penny.