How much do you have to spend, to get a good Sub?

Shelby+Kroll Woofer Monitors are designed for use as a music sub. 10" 300w Bash amp that will play fast, low and clean.

For music, I really enjoy my Vandersteen 2Wq. I have a pair of them now, but started with one. It is designed for music, not home theater. You should review the product info on the Vandersteen web site, since this sub has a unique hook-up scheme. This helps to smoothly integrate your mains with the sub. You will need separate amp and preamp, or an integrated amp with pre-outs and power-amp inputs. The sub costs about $1500 new, and you will need to purchase an in-line filter for another $125 afterwards. It has adjustable Q, but no room EQ. Instead, it is designed for best performance when placed in a corner, which is where most people put their subs anyway. Also, your mains will have to have decent output down to 40Hz. I like these so much that I base all system upgrades around them. They are in my rig to stay.

A used REL can do the job...mine was missing grill cloth (easily remedied) but otherwise is fine, works perfectly, and I can't imagine not having one. It's a Q150E Ebay score that cost around $200 a couple of years ago.