I'm working on a Master of Many Forms. Given that not all forms you can turn into creatures with high strength but not too spectacular natural attacks (Giants and such), I want to arm him with a weapon. My eye fell on using clubs, carried around in a Vestment of Many Styles on a Wildling Clasp with the effect of a Handy Haversack enchanted into it.
Now, I could use an enchantment to scale a club to my size (large, huge and so on), but this prevents Shillelagh being cast on it. So the solution sounded simple to me: carry bigger clubs.
The damage and weight are not difficult to calculate for bigger weapons, but what about cost? A Medium club has no cost, so how about bigger ones? I don't think the material used for Shillelagh (oak wood) has any specific cost to it, so I believe that's not an issue here.