How do you estimate 'production cost' for intangible/digital assets?
Bitcoin is not a "product", this logic does not apply. Product, from
production. Production is a process of combining various
material inputs and immaterial inputs (plans, know-how) in order to make something for consumption (the output).
Bitcoins are not "produced", they are
discovered through mathematics. Bitcoins also cannot be owned, only
controlled. Bitcoins are just information, little bits of math. That's why brain wallets are possible. You can't "memorize" a product and sell that memory, now can you? You can with bitcoin, because it's just releasing control of a bit of information.
Just as an aside, this is why it's insane to try and regulate bitcoin the way any other form of money has been regulated. Once you truly comprehend everything I've just explained, you may begin to understand why day-to-day fiat exchange price does not matter at all.