The other thing you should consider is that if you do buy a fully functional sword or machete and accidentally kill someone with it, aren't you going to get in trouble with the authorities, even if it was self-defense?? Some of the weapons mentioned above would be appropriate for medieval battles but ask yourself if you really have the stomach for a real life sword fight, something most of us have never seen in our lifetime except in movies.
The best option would be not to go there, however if you have no choice, consider nonlethal options like a Taser, Mace, pepper spray or a baseball bat. If you want a crude stick type weapon, get a police baton, escrima sticks or 2-3 ft of copper plumbing pipe. Or buy the cheapest machete you can find and file the edge off of it so it won't cut, even without a sharp edge, getting hit with a long thin piece of steel, the amount of force exerted on a small area will produce a lot of injury.
I use my machetes and kukris and goloks for cutting plants, but I don't think I would want to be held by the police for chopping off someone's arm, even if it was self defense.