I may get flamed, but I like the Klipsch RSW 12 or 15, which you should be able to find used for around $600 to $800
Sleeper subs in the $500 range....
Besides HSU,Adire,etc...what subs out there...new or old...excel at music in this price class? My room is 20 x 16...I am contemplating older Velodyne F series...