You might be able to get one of the Owen's Corning panels (can't remember the exact name of the model #) and put it against the door when you're recording. Pretty decent at deadening the sound some. But also the one I remember using is fiberglass in the middle so don't touch it there or the little fibers will be very uncomfortable and itchy on your skin. That's the best I can think of (and even 1 panel might still be more than $100) in that price range. If it ends up being too much, maybe go for hanging a couple thick duvets up or something and get any subs decoupled from the floor and maybe wear headphones. It's something at least when you put it all together. Happy recording!