SULers use spectra for guy-lines, bear bagging, etc.. Found out arborists use this stuff also.
This site has 1.75mm coated knottable dyneema, or pure spectra for $23/$22 per 180'. 2.2mm also available.
It's not exactly the same as the aircore spectra at the BPL shop, and not as strong, at 400lbs breaking strength, but 1/4 the price per foot.
http://www.wesspur.com/Throw-line/zing-it-throw-line.html#bags

