#RAW only things with a Gold Value are costs
The [spellcasting rules on components](https://www.dndbeyond.com/compendium/rules/basic-rules/spellcasting#MaterialM) state:

>A character can use a **component pouch or a spellcasting focus in place of the components specified for a spell**. But if a cost is indicated for a component, a character must have that specific component before he or she can cast the spell.

You cannot replace material components that have a listed cost however.

##What is a listed cost?
By RAW a listed cost is only for item with a gold value. "A diamond worth at least 50gp" for example.