Subwoofers are a terrible thing. If you buy cheap, you buy disappointment and if you buy just a bit better, one gets sucked into the very expensive upgrade game.
One is best served buying the best they can afford and later buy a second one with a watchful eye on a possible third. And painfully I post, this is not an exaggeration. I wish I could be encouraging, but I can't, other than to say, welcome to AVS and the wonderful world of subwoofers.
I always encourage one to check out the budget subwoofer threads running and the ULF thread as between these threads, one will get a heck of a lot of experience reading what others have to say on the matter.