I buy one of those old fashioned ‘Rastafarian’ mop heads from the market for a couple of quid. I take the threads out, dunk them in a tub of used tea bags for a day to take away the whiteness (I know, I know - I’m far too precious) and then dry them and cut them in half. You then have a couple of years’ supply of perfect length, very soft tying-in string.
Well, without knowing how long it is and how much they charge I can’t really say? 😉 .... and it’s seems that even they don’t know how long it is https://www.niwaki.com/store/coir-twine/but it appears to be suitable for tieing up sweet peas and annoying brothers and for those purposes it’s probably worth it’s weight in gold. My guess is that the majority of these lumps of twine are sold to folk ‘dressing’ potting sheds for tv programmes or films about gardening or rural pursuits.