So, via this thing: http://www.thingiverse.com/thing:104868 it seems someone has found some decent nylon trimmer line to print with.
$22 for 3 lbs of filament? I’m sure it’s no taulman Nylon, but still! (Be aware that this also has the possibility of contaminants, additives, and things that could be bad for your health)
The size is equal to 1.75mm filament.