If you don't want to spend too much then your options are every limited, its never a good idea just to replace one component in a drive system where all others are also worn. So I would soak it clean, there are many special cleaners of you can use diesel etc, turps etc, if you wish: leave it in to soak change the cleaning fluid until its no longer goes black when you stir it, let it hang bone dry, then re-lub it. Depending on the amount of rust it might be worth touching those areas if on the outside links with a brass wire brush before you clean it.