It's interesting that, when we put a label of "priceless" onto something, it always means - or is supposed to mean - "so valuable it can't be assigned a price". Never, when you say the word, you are expected for it to mean "of so low value that you can take it for free" or "worthless" - there's even a different word for it at the tip of one's tongue. When you do mean it, it only causes confusion, despite the word being fully capable of portraying both sides of your appreciation of an object.
The same is the situation within the two other languages I speak: Russian separates "бесценный" (behs-TSEN-nyi, literally "priceless") and "бесполезный" / "никчёмный" (behs-poh-LEZ-nyi / nih-KTSCHØM-nyi, both literally "useless"), and German does it with "unbezahlbar" (literally "unpurchasable") and "wertlos" (literally "worthless").
It makes sense that we've assigned price to the high end of the scale and worth - the the low end, - in more than one way. What inspires my curiosity is the way we've communicated this set of ideas through words.
Is price or puchasing possibility more important than worth? Can we present an object of as of so high worth that one can't become in possession of it, or that another isn't willing to part with it? It now doesn't relate to money, and as such, we have only a few ways to measure the worth, if any at all. Those are questions I don't have an answer to. I thought it would be an interesting thing to share about the way we use language.