There are two different ways of reading the rules regarding spell components and spells in general — "fiction first" (narrative approach) and "rules first" (mechanical approach). There is no "right" one, the choice depends on your own playstyle, what people at this particular table want, and other factors.
For instance, Find the Path spell requires
an object from the location you wish to find
From the "rules first" perspective you can substitute this object with your focus, since it has no price specified. However, this makes no sense for the "fiction first" point of view, because the result of the spell probably depends on the object being used, and your spellcasting focus is not a thing from the location you're searching for.
Regarding the Scrying spell, if you prefer the "rules first" approach then the resolution is clear (but maybe kind of boring) — the spell just takes effect, no mirror nor crystal ball is required, because magic.
If you choose the "fiction first" approach then the spell probably should require some kind of "screen" for scrying. But asking for a full-price crystal ball would be disappointing for the player, since it'd be basically nullifying the character's prominent feature. Instead, I suggest you to allow using any reflective surface in this case — a mundane mirror, a water puddle, anything.
Or just ask the player "how do you do that"? It's their magic, after all.