The cheap rolls of speaker wire sold in stores under $15 will either be all aluminum or will be Copper for + and Aluminum for - or Aluminum for both + -.
Monster Car Audio has the best speaker wire ive ever used for car installations as its pure copper and def not cheap.
The chances are speaker wire laying around the house/junk drawer is garbage aluminum wire i wouldnt use.
For the price of a extension cord at walmart, id just head there and buy that.