You are probably right that the leg is broken or at least the joint. If I had to guess, either there isn't a vet in your area that can do anything about it or the costs will be prohibitively expensive. I wish there was an easy fix but there probably isn't. I may be wrong and in that case, there is no harm in calling a vet in your area who has worked with amphibians in the past and seeing what he or she thinks the options are. Who knows, maybe it can make a complete recovery.

If keeping the toad as a pet is an option you can probably recover it to the point that it can live a longer than average life in captivity. In the wild with a busted leg the toad just doesn't have much of a chance. I cannot think of a reason why you can't use neosporin on the tissue wounds -- try to get the kind that does not have an added anaesthetic. It's probably not what a vet would prescribe but will probably ward off infection.