You should probably only use copper wire. I would buy cat-5 solid network cable, and take it apart to get the individual, insulated strands. This is very cheap, because there are 8 strands in the jacket, and it's flexible. If you can't find it for free, you can get 50 or 100 feet of this or cat-3 at home depot. Either would be fine.
What you don't want is normal phone wire, because it's too thick and stiff. 22 guage is prolly the biggest you want, 24 being smaller and better.