i know you people will know the answer to this

[fleagirl]

local folks: i need some soundproofing foam (or something similar) to cover an area about the size of a standard interior door. basically, something not too heavy, with decent (not professional or anything) soundproofing qualities, about 2'-3' x 6.5'? or so? where should i go to get something like that? or does anyone have any laying about they'd like to offload?

eta: alternate ideas for cheaply adding a layer of soundproofing over an otherwise unused door are appreciated, too!