I've used 1:10 in the past MF (1 part molasses)
Your local stockfeed or equestrian store (I suppose thats what you would call it) would probably have it in a useful size pail (normally 13-20kg in most cases I think)
I bought a several 1.25L of coles 'diet coke' for 25c or 35c a bottle - strips rust off almost as good as it rots teeth out haha
Black and gold white vinegar is also another alternative, as is electrolysis, but Molasses is probably the best
