Cheap 8" sub

Looking for a cheap ($50 - $60) 8" sub, needs to have a 4 ohm final load. No crazy RMS, this is gonna be replacing a logitech sub used for a desktop setup. The big thing is that the sub needs to be able to play down into the low 30's at least. The current sub sounds like total ***** below like 50hz. I even made a new box for it that's 0.7 cubes tuned to 35hz and it can't play anything under 50hz without having a tremendous amount of port noise (the original box for it did the exact same thing).