under $100 subs...id recommend the pioneer 305...you can get it at etronics for 55 bucks

100-150 range...
alpine type r...edesign audio K series or adireaudio shiva...
all are considered very SQ oriented subs..

u can also find the idq subs...but im not too sure about their prices...
those subs work very well in small sealed boxes...and doesnt require much to go ported...