For my JCB strimmer i use cable from bnq, it looks like speaker cable, for my use i dont need blades, but the thick bnq wire lasts very long,
as has been said, depends what you want to cut, i can get away with cutting small branches half an inch or so without the wire breaking or it getting tangled etc..
dunno about buying an ex-council one as when we used them they were ragged to buggery and often not serviced, may be different in your area.
if you do decide to go with cable id deffo recommend the black/yellow cable from bnq, it is very heavy duty, ive still got a big reel left and ive been using it all last spring/summer and this spring/summer