once btc becomes PoS 'mined' where it doesnt cost a penny to mine it.. down will drop the cost and down will come the price.
Why on earth do you think that's gonna happen? Proof of stake is, as of now, still unproven as a reliable method to secure the chain. Proof of work does, the only drawback being high energy consumption. Bitcoin will never be proof of stake. It'll be long gone by the time developers even consider going pos.