You're best off selling shares in big chunks to a single or a few buyers because each transaction requires signatures and a process from Bnk to the future.
Regarding price, they're worth what someone will pay for them. I don't know of any price discovery mechanism other than asking whoever sold / bought on this thread last what they got for / paid for their shares then negotiating with potential buyers / putting offers out there.
I feel we would benefit from a place to connect buyers & sellers, but this thread is the best option for now.
You just need to invite offers and see who gets in touch. Bear in mind it's easier if buyers are already registered on Bnk to the future, and there's a 5% fee for their transfer service which includes escrow.