Classic Sub For A Reasonable Price

A few hundos? Ah, no, if your looking for an amazing sub, save up about 5  hundos more , and wait until you can invest for about $675 -$850 and get a real subwoofer.
Hsu, Rythmic, SVS, Monolith, PSA, JTR all sell direct to you.
I have been reading about subwoofers for many months at AVS Forum:
https://www.avsforum.com/forum/113-subwoofers-bass-transducers/

These people are serious about subs, and you can learn alot from reading the threads.
They are going to want to know the exact dimensions of room and ceiling height .
Are you going to use this for double duty with hometheater? If so , maybe you would need a 15 inch woofer.? ($800-$1500)
Can you buy one subwoofer now and add a second one down the road?

Here is the Monolith, they do go on sale occasionally . Now it runs for $800.
https://www.monoprice.com/product?p_id=24457&gclid=Cj0KCQjwrJ7nBRD5ARIsAATMxssRgSbOlwXOQSQ5a8YHshDUrNFZxCG22SN-8S9e92DM_ZUqnUmko4oaAuWwEALw_wcB

a 12 inch woofer is the place to start IMHO if you want deep bass.
The Monolith will give you deep, tight, bass, and be thunderous for movies,  but as you can see , serious subwoofers cost serious money.
Every other company I mentioned, the 12 inch subs will run about the same price.
Good luck to you.

I mention this often as it serves to make others feel bad, but I bought both of my RELs at about a year apart (now at least 5 or so years ago) for 200 bucks each after keeping an eye out for ’em on Ebay for a while. Both are the UK made versions, a Q150e and a Q108MKII in near perfect condition as one needed a grill cloth...both are absolutely great, and nice used RELs show up fairly often. I make my own REL cables from Canare "star quad" and the only maintenance required is tightening the speaker bolts from time to time, and dusting. The "12 inch woofer" necessity claim is baloney as there's a lot more to great design than speaker size. 

It all depends on what you are looking for.  For modern speakers being driven by appropriate electronics playing anything other than electronica, EDM, heavy bass rap, or serious pipe organ music, REL makes some great subs that typically integrate well in most residential rooms.  Two is usually a better choice to maximize the effects of room resonance, but one can be effective if you listen privately from the same position.
If your taste runs to the bass-heavy categories I described, and/or you want to feel the thump in your chest and have your pant cuffs flutter in the breeze, other options are available.