If your old cable is in reasonably good shape and you want to save money,
clean up the ends and solder new lugs on. Unless it's physically broken, the
copper stranding won't change in resistance no matter how old it gets.
Copper is copper. Flux, like what they sell for pipes, helps make the solder
flow faster and keep insulation damage down, too.

One of the best mods I made to my Westy was soldering in an additional 10
AWG wire from alternator post to starter, and the same thing from the
battery positive post to the aux battery relay. Especially in the early
years (mine's an '84) the charging wires were marginal in capacity, leading,
in my case, to lousy charging of both batteries. Probably the easiest,
cheapest, most effective mod/repair I've done.