I would recommend buying a cheaper version; SO and SJ, are overkill for speaker wire, unless you get them really cheap. Ask about cheaper "S" version cords at the Depot or Lowes, like SPT or SP.
Their are many designations for portable power cord, SO and SJ are 'general' starting points.
SO cord: S= Heavy duty service to 600V rubber insulated, stranded copper conductors. the O= oil resistant .
SJ cord: SJ = Junior Hard Service to 300V, same as above but with thinner jacket.
If you have a Harbor Freight nearby; buy a cheap 12AWG extension cord, and cut the ends off.
That may be cheaper than paying per foot at the Depot.