By - Azmaeth
Perhaps you're mixing up spells that have a monetary cost. Your arcane focus means you can ignore material components for spells unless the material components state they have a monetary value. For instance: Chromatic Orb requires a diamond worth 50gp. Your arcane focus would not count for that.
I'm a DM, and my wild magic sorcerer has an Arcane focus that is a sprig oh his holy tree, but there's a cradle in the top that I've told him a gem would fit into (because I like the idea of his focus evolving, if he wants it to)
So what if he puts a diamond worth 50gp in it?
He can use it like that just fine, but keep in mind it wouldn't gain any benefit from the focus itself, since it's not the material component.
And the diamond would be consumed when casting the spell.
Chromatic orb doesn't consume the component, only spells where it explicitly states the component is consumed is it removed. It's more of a barrier than a cost to the spell.
You don't have to pay attention to your spellcasting focus's cost.
Can you give an example in the rules? I've never seen a case where your spellcasting focus needs to cost a certain amount.
A pot isn’t limited or destroyed on use (hopefully) either, but it still has a cost. What’s the point here?
I dint exactly understand the way you explained it. But I'd assume different focuses would have different effectiveness based on what it is? Like a magic crystal in a staff made from and ancient tree would cost waaaay less to cast something from than a wand made from normal ass wood. Is that what you were looking for?
If you're talking about material components for spells with a listed price, they're a separate thing to spell focuses and it'll say in the cost if they're consumed by the spell (as with most resurrection spells).
You also have to check the wording of the material costs.
If it has a gold value, but doesn't say that the components get consumed, then it only costs money the first time you cast the spell.
As long as you keep the component in your pack, you can recast the spell as much as you want.
I think it is a little like when a martial character has to spend some gold for better armor. It gives you a way to upgrade your character after your first payday.
It is also an easily carried valuable item that you wave around in front of bandits. If they can snatch it and run it can give you a consequence of getting knocked out that doesn't kill your character.
The focus items are sort of like a sling or bow. You need it to make the projectiles (magic) go farther (have particular effects),but it's not consumed. You just can't really launch the projectiles well without it.
The cost items are sort of like the ammunition. When you toss it, it's gone, but depending on what it is, it'll make a different effect.
In general for low cost things it's assumed that you're able to gather /buy the bits you need and keep them in your components pouch. If you're consuming a lot of something, the dm should probably be dinging you for those low costs.