Pricerange:  6.00 € (100 meter)

http://www.hornbach.at/shop/Decofil-Mamutec-Polyamid-0-7-mm-100-m/8442249/artikel.html?WT.svl=artikel_img

Mamutec Decofil perlon (PolyAmide) thread instead of fishing line.

The perlonwire is thicker then fishing line 0.7mm is the one I tested on the SmartRap printer.
This perlon does not stretch as much as nylon fishingline. (braided "spectra" line stretches even less but because it is thinner it tends to cut into PLA shaftcouplers)

Also available in 0.4mm and 1mm diameter. (instead of 0.4mm it's  more easy to buy fishingline, 1mm is mostlikely to stiff for 1cm shaftcouplers but might be usefull on other projects with thicker shaft)

Maybe thicker fishing line works the same, just give it a try if you have some available.