K-Mart/Wal-Mart sells 400' of e-string for $2.99.
  

  K-Mart and Wal-Mart both sell 5/32 inch vinyl coated clothesline 
  which has eight .012" very hard steel wires running through a sheath 
  of smooth green, see-through vinyl. This stuff is made by the 
  "Lehigh Group" (http://www.lehighgroup.com).

  The individual strands of this clothesline makes excellent music 
  wire. 90% of the strings I break are the thinnest one & this wire 
  works wonderfully on guitars, banjos, octave mandolin etc etc. It's 
  sound and playability is not a bit different from that of 
  commercially made strings of the same gauge.
  
  It's slightly inconvenient to have to peel off the vinyl coating and
  extract the wire, but well worth the effort.

  Dennis Havlena - W8MI
  northern Michigan