We have a Poundland shop in Hereford, and I was poking about seeing what they had cheap, and came across a pack of four nylon tent style guys, with the plastic tensioning buckle thingies, each 3.5metres long, about 3mm nylon cord, in vivid yellow. £1.
Though I would share as if you have a local one, worth seeing if they have some.
These are the fellas. Might help anyone interested find them elsewhere.