Cheap alturnatives inc
you either add weight, to reduce vibration noise
bitumen tape (smelly but cheap - best used as a sandwidge between layers)
Neoprene rubber - wetsuit not drysuit version ideally
carpet tile - adds weight and absorbs (can be colour matched to build)
and/or use an open cell foam/material to absorb sound energy as it moves between the air pockets
felt - the underfloor insulation type or just craft shop stuff
acoustic ceiling tile
'green' scouring pad (not really that good)
hoover bag
3-5 layers of streached tights
layers or sandwidge panels work best (in to outside)
perforated layer - open cell thickness - solid panel
Blocking up all the holes also works well - but then heat is an issue
