[@KoL]
What would cause one Silver Eyes use to be more 'costly' than another. Is it mass? Volume? Complexity? Are certain materials simply more 'costly' than others? How exactly would one measure how difficult it is to create one thing, compared to another?

Edit:
Extra question: are the Silver Eyes limited to matter, or can they also create energy? Like, could you use your silver eyes to create an electromagnetic field? Or a gravity well?