I have a possibility in mind...
Does it smell?
Does it burn (might be sooty)?
Is it light in weight for its size (does it float on water)?
Haven't tried burning it as it seems delicate and I don't want to lose the glass like crystal inside it doesn't smell it doesn't float in water but it is lighter than it looks. To touch it feels coral like and turned on its broken edge you can see layers of the white shell like layer and opal crystals as if it was crushed.
Not ambergris, then.
I don't know what to suggest, other than bringing or sending it in to the Angela Marmont Centre (email them first).
Have you an email? I have more photos of the object from different angles.
Just a thought but it has similar qualities to Crinoid or even Siphusauctum, I believe it is part of the calyx and stem. The stem is hollow and you can also see that there was a hollow void where the digestive tract would be, what are your thoughts?
That's an interesting link; well done for finding it and for your pursuit of the truth.
Seeing your extra photo, I see what you mean about a goblet shaped calyx. Your specimen appears, however, to be thin-walled - so it is not a crinoid. It is also considerably larger and also certainly much more recent than the Burgess Shale organisms. Tunicates are rarely preserved as fossils, and in those cases they are completely flattened (like the Siphusauctum from the Burgess Shale) - not somewhat squashed like yours.
One or two things (eg. surface texture) make me think it could be man-made.
Overall, I'm still struggling....
I really think it needs to be taken/sent to the Angela Marmont Centre (as above) - for somebody to look at the surface, structure and perhaps chemical composition closely.