Kevlar or Spectra kite line works great for most applications.

Very strong. 1 to 3% stretch and lighter than steel.

You get it in spools and is very cheap in bulk ($15 or so for 200 feet).

I like 200 lb kevlar for nearly all my glo power stuff, but it's way overkill. Many different weights and lengths available from kite shops (Hang em High fabrics or "Into the Wind")

Be sure not to get dacron or nylon, as that has too much stretch for pull pull.