Simple answer is don't find these in the editor. These are Gizmos which are created/edited in XML outside the editor.
This "could" be done but its a VERY VERY advanced area of HL scripting where you will be using the Authoring kit.
I would start with a more simple wondrous item concept that I used to make a dorjes which is a Wand like item for Psionics. You can see the XML here on
GitHub.
Yes the main issue is that the cost can not be calculated until after the item is added to the character.