Kingdom Key is 25$
Kairi Keyblade is 35$
Usually they don't get too high, the most expensive thing I have sold would be Demyx's Sitar for 200, but only because it was so big and hard to make.
I have also sold Oathkeeper and Oblivion as a set for 100$ and Oblivion has an actual chain in it.
If you have any questions on pricing or if you want to know if I can make something, I try and keep it to just Kingdom Hearts and Final Fantasy Weapons.